How can I convert a string to boolean in JavaScript?

Kevin Source

Can I convert a string representing a boolean value (e.g., 'true', 'false') into a intrinsic type in JavaScript?

I have a hidden form in HTML that is updated based upon a user's selection within a list. This form contains some fields which represent boolean values and are dynamically populated with an intrinsic boolean value. However, once this value is placed into the hidden input field it becomes a string.

The only way I could find to determine the field's boolean value, once it was converted into a string, was to depend upon the literal value of its string representation.

var myValue = document.myForm.IS_TRUE.value;
var isTrueSet = myValue == 'true';

Is there a better way to accomplish this?

javascript

Answers

answered 10 years ago FlySwat #1

 var myBool = Boolean.parse("true");

or

var myBool = Boolean("true");

or

var myBool = !!"true";

Not sure if the first one is IE specific.

answered 10 years ago guinaps #2

Do:

var isTrueSet = (myValue == 'true');

You could make it stricter by using the identity operator (===), which doesn't make any implicit type conversions when the compared variables have different types, instead of the equality operator (==).

var isTrueSet = (myValue === 'true');

Don't:

You should probably be cautious about using these two methods for your specific needs:

var myBool = Boolean("false");  // == true

var myBool = !!"false";  // == true

Any string which isn't the empty string will evaluate to true by using them. Although they're the cleanest methods I can think of concerning to boolean conversion, I think they're not what you're looking for.

answered 10 years ago Jared Farrish #3

Remember to match case:

var isTrueSet = (myValue.toLowerCase() === 'true');

Also, if it's a form element checkbox, you can also detect if the checkbox is checked:

var isTrueSet = document.myForm.IS_TRUE.checked;

Assuming that if it is checked, it is "set" equal to true. This evaluates as true/false.

answered 10 years ago Jonny Buchanan #4

Your solution is fine.

Using === would just be silly in this case, as the field's value will always be a String.

answered 10 years ago staticsan #5

You need to separate (in your thinking) the value of your selections and the representation of that value.

Pick a point in the JavaScript logic where they need to transition from string sentinels to native type and do a comparison there, preferably where it only gets done once for each value that needs to be converted. Remember to address what needs to happen if the string sentinel is not one the script knows (i.e. do you default to true or to false?)

In other words, yes, you need to depend on the string's value. :-)

answered 10 years ago JW. #6

If there's some other code that's converting the boolean value to a string, you need to know exactly how that code stores true/false values. Either that or you need to have access to a function that reverses that conversion.

There are infinitely many ways to represent boolean values in strings ("true", "Y", "1", etc.). So you shouldn't rely on some general-purpose string-to-boolean converter, like Boolean(myValue). You need to use a routine that reverses the original boolean-to-string conversion, whatever that is.

If you know that it converts true booleans to "true" strings, then your sample code is fine. Except that you should use === instead of ==, so there's no automatic type conversion.

answered 10 years ago Shadow2531 #7

You can use regular expressions:

/*
 * Converts a string to a bool.
 *
 * This conversion will:
 *
 *  - match 'true', 'on', or '1' as true.
 *  - ignore all white-space padding
 *  - ignore capitalization (case).
 *
 * '  tRue  ','ON', and '1   ' will all evaluate as true.
 *
 */
function strToBool(s)
{
    // will match one and only one of the string 'true','1', or 'on' rerardless
    // of capitalization and regardless off surrounding white-space.
    //
    regex=/^\s*(true|1|on)\s*$/i

    return regex.test(s);
}

If you like extending the String class you can do:

String.prototype.bool = function() {
    return strToBool(this);
};

alert("true".bool());

For those (see the comments) that would like to extend the String object to get this but are worried about enumerability and are worried about clashing with other code that extends the String object:

Object.defineProperty(String.prototype, "com_example_bool", {
    get : function() {
        return (/^(true|1)$/i).test(this);
    }
});
alert("true".com_example_bool);

(Won't work in older browsers of course and Firefox shows false while Opera, Chrome, Safari and IE show true. Bug 720760)

answered 10 years ago ander #8

I think this is much universal:

if (String(a) == "true") ...

It goes:

String(true) == "true"     //returns true
String(false) == "true"    //returns false
String("true") == "true"   //returns true
String("false") == "true"  //returns false

answered 9 years ago Icaro Dourado #9

if (String(a) == "true"){
  //true block
} else {
  //false block
}

answered 9 years ago Steven #10

stringToBoolean: function(string){
    switch(string.toLowerCase().trim()){
        case "true": case "yes": case "1": return true;
        case "false": case "no": case "0": case null: return false;
        default: return Boolean(string);
    }
}

answered 9 years ago PixelSlave #11

Just do a:

var myBool = eval (yourString);

Examples:

alert (eval ("true") == true); // TRUE
alert (eval ("true") == false); // FALSE
alert (eval ("1") == true); // TRUE
alert (eval ("1") == false); // FALSE
alert (eval ("false") == true); // FALSE;
alert (eval ("false") == false); // TRUE
alert (eval ("0") == true); // FALSE
alert (eval ("0") == false); // TRUE
alert (eval ("") == undefined); // TRUE
alert (eval () == undefined); // TRUE

This method handles the empty string and undefined string naturally as if you declare a variable without assigning it a value.

answered 9 years ago Thomas Eding #12

Boolean.parse = function (str) {
  switch (str.toLowerCase ()) {
    case "true":
      return true;
    case "false":
      return false;
    default:
      throw new Error ("Boolean.parse: Cannot convert string to boolean.");
  }
};

answered 8 years ago cypher #13

The following would be enough

String.prototype.boolean = function() {
    return "true" == this; 
};

"true".boolean() // returns true "false".boolean() // returns false

answered 8 years ago thdoan #14

The Boolean object doesn't have a 'parse' method. Boolean('false') returns true, so that won't work. !!'false' also returns true, so that won't work also.

If you want string 'true' to return boolean true and string 'false' to return boolean false, then the simplest solution is to use eval(). eval('true') returns true and eval('false') returns false. Keep in mind the performance implications when using eval() though.

answered 7 years ago risingfish #15

Hands down the easiest way (assuming you string will be 'true' or 'false') is:

var z = 'true';
var y = 'false';
var b = (z === 'true'); // will evaluate to true
var c = (y === 'true'); // will evaluate to false

Always use the === operator instead of the == operator for these types of conversions!

answered 7 years ago Vitim.us #16

function returnBoolean(str){

    str=str.toString().toLowerCase();

    if(str=='true' || str=='1' || str=='yes' || str=='y' || str=='on' || str=='+'){
        return(true);
    }
    else if(str=='false' || str=='0' || str=='no' || str=='n' || str=='off' || str=='-'){
        return(false);
    }else{
        return(undefined);
    }
}

answered 7 years ago Luke #17

Warning

This highly upvoted legacy answer is technically correct but only covers a very specific scenario, when your string value is EXACTLY "true" or "false" (MUST be lowercase as well).

An invalid json string passed into these functions below WILL throw an exception.


Original answer:

How about?

JSON.parse("true");

or with jQuery

$.parseJSON("true");

answered 7 years ago hajikelist #18

I've found that using '1' and an empty value '' for boolean values works far more predictably than 'true' or 'false' string values... specifically with html forms since uninitialized/empty values in Dom elements will consistently evaluate to false whereas any value within them evaluates to true.

For instance:

<input type='button' onclick='this.value = tog(this.value);' />

<script type="text/javascript">

    function tog(off) {
        if(off) {
            alert('true, toggle to false');
            return '';
        } else {
            alert('false, toggle to true');
            return '1';
        }
    }   
</script>

Just seemed like an easier road, so far it's been very consistent/easy... perhaps someone can determine a way to break this?

answered 7 years ago imjustmatthew #19

Like @Shadow2531 said, you can't just convert it directly. I'd also suggest that you consider string inputs besides "true" and "false" that are 'truthy' and 'falsey' if your code is going to be reused/used by others. This is what I use:

function parseBoolean(string) {
  switch (String(string).toLowerCase()) {
    case "true":
    case "1":
    case "yes":
    case "y":
      return true;
    case "false":
    case "0":
    case "no":
    case "n":
      return false;
    default:
      //you could throw an error, but 'undefined' seems a more logical reply
      return undefined;
  }
}

answered 6 years ago Scrimothy #20

@guinaps> Any string which isn't the empty string will evaluate to true by using them.

How about using the String.match() method

var str="true";
var boolStr=Boolean(str.match(/^true$/i)); 

this alone won't get the 1/0 or the yes/no, but it will catch the TRUE/true, as well, it will return false for any string that happens to have "true" as a substring.

EDIT

Below is a function to handle true/false, 1/0, yes/no (case-insensitive)

​function stringToBool(str) {
    var bool;
    if (str.match(/^(true|1|yes)$/i) !== null) {
        bool = true;
    } else if (str.match(/^(false|0|no)*$/i) !== null) {
        bool = false;
    } else {
        bool = null;
        if (console) console.log('"' + str + '" is not a boolean value');
    }
    return bool;
}

stringToBool('1'); // true
stringToBool('No'); // false
stringToBool('falsey'); // null ("falsey" is not a boolean value.)
stringToBool(''); // false

answered 6 years ago mbeasley #21

Boolean.parse() does exist in some browser implementations. It's definitely not universal, so if that's something that you need than you shouldn't use this method. But in Chrome, for example (I'm using v21) it works just fine and as one would expect.

answered 6 years ago jerone #22

I've been using this snippet to convert Numbers and Booleans:

var result = !isNaN(value) ? parseFloat(value) : /^\s*(true|false)\s*$/i.exec(value) ? RegExp.$1.toLowerCase() === "true" : value;

answered 6 years ago AndreasPizsa #23

The expression you're looking for simply is

/^true$/i.test(myValue)

as in

var isTrueSet = /^true$/i.test(myValue);

This tests myValue against a regular expression , case-insensitive, and doesn't modify the prototype.

Examples:

/^true$/i.test("true"); // true
/^true$/i.test("TRUE"); // true
/^true$/i.test("tRuE"); // true
/^true$/i.test(" tRuE"); // false (notice the space at the beginning)
/^true$/i.test("untrue"); // false (some other solutions here will incorrectly return true
/^true$/i.test("false");// returns false
/^true$/i.test("xyz");  // returns false

answered 6 years ago BishopZ #24

My take on this question is that it aims to satisfy three objectives:

  • Return true/false for truthy and falsey values, but also return true/false for multiple string values that would be truthy or falsey if they were Booleans instead of strings.
  • Second, provide a resilient interface so that values other than those specified will not fail, but rather return a default value
  • Third, do all this with as little code as possible.

The problem with using JSON is that it fails by causing a Javascript error. This solution is not resilient (though it satisfies 1 and 3):

JSON.parse("FALSE") // fails

This solution is not concise enough:

if(value === "TRUE" || value === "yes" || ...) { return true; }

I am working on solving this exact problem for Typecast.js. And the best solution to all three objectives is this one:

return /^true$/i.test(v);

It works for many cases, does not fail when values like {} are passed in, and is very concise. Also it returns false as the default value rather than undefined or throwing an Error, which is more useful in loosely-typed Javascript development. Bravo to the other answers that suggested it!

answered 6 years ago jackvsworld #25

Building on Steven's answer above, I wrote this function as a generic parser for string input:

parse:
  function (value) {
    switch (value && value.toLowerCase()) {
      case null: return null;
      case "true": return true;
      case "false": return false;
      default: try { return parseFloat(value); } catch (e) { return value; }
    }
  }

answered 5 years ago purab #26

You even do not need to convert the string to boolean. just use the following: var yourstring = yourstringValue == 1 ? true : false;

answered 5 years ago dalimian #27

i wrote a helper function that handles your cases (and some more). Feel free to alter it to your specific needs

/**
 * @example
 * <code>
 * var pageRequestParams = {'enableFeatureX': 'true'};
 * toBool(pageRequestParams.enableFeatureX);  // returns true
 *
 * toBool(pageRequestParams.enableFeatureY, true, options.enableFeatureY)
 * </code>
 * @param {*}value
 * @param {Boolean}[mapEmptyStringToTrue=false]
 * @param {Boolean}[defaultVal=false] this is returned if value is undefined.
 *
 * @returns {Boolean}
 * @example
 * <code>
 * toBool({'enableFeatureX': ''        }.enableFeatureX);          // false
 * toBool({'enableFeatureX': ''        }.enableFeatureX, true);    // true
 * toBool({                            }.enableFeatureX, true);    // false
 * toBool({'enableFeatureX': 0         }.enableFeatureX);          // false
 * toBool({'enableFeatureX': '0'       }.enableFeatureX);          // false
 * toBool({'enableFeatureX': '0 '      }.enableFeatureX);          // false
 * toBool({'enableFeatureX': 'false'   }.enableFeatureX);          // false
 * toBool({'enableFeatureX': 'falsE '  }.enableFeatureX);          // false
 * toBool({'enableFeatureX': 'no'      }.enableFeatureX);          // false
 *
 * toBool({'enableFeatureX': 1         }.enableFeatureX);          // true
 * toBool({'enableFeatureX': '-2'      }.enableFeatureX);          // true
 * toBool({'enableFeatureX': 'true'    }.enableFeatureX);          // true
 * toBool({'enableFeatureX': 'false_'  }.enableFeatureX);          // true
 * toBool({'enableFeatureX': 'john doe'}.enableFeatureX);          // true
 * </code>
 *
 */
var toBool = function (value, mapEmptyStringToTrue, defaultVal) {
    if (value === undefined) {return Boolean(defaultVal); }
    mapEmptyStringToTrue = mapEmptyStringToTrue !== undefined ? mapEmptyStringToTrue : false; // default to false
    var strFalseValues = ['0', 'false', 'no'].concat(!mapEmptyStringToTrue ? [''] : []);
    if (typeof value === 'string') {
        return (strFalseValues.indexOf(value.toLowerCase().trim()) === -1);
    }
    // value is likely null, boolean, or number
    return Boolean(value);
};

answered 5 years ago Andreas Dyballa #28

    MyLib.Convert.bool = function(param) {
         var res = String(param).toLowerCase();
         return !(!Boolean(res) || res === "false" || res === "0");
     }; 

answered 5 years ago user3638793 #29

Here is my 1 liner submission: I needed to evaluate a string and output, true if 'true', false if 'false' and a number if anything like '-12.35673'.

val = 'false';

val = /^false$/i.test(val) ? false : ( /^true$/i.test(val) ? true : val*1 ? val*1 : val );

answered 5 years ago zobier #30

I use the following:

function parseBool(b) {
    return !(/^(false|0)$/i).test(b) && !!b;
}

This function performs the usual Boolean coercion with the exception of the strings "false" (case insensitive) and "0".

answered 5 years ago Dead.Rabit #31

I'm a little late, but I have a little snippet to do this, it essentially maintains all of JScripts truthey/falsey/filthy-ness but includes "false" as an acceptible value for false.

I prefer this method to the ones mentioned because it doesn't rely on a 3rd party to parse the code (i.e: eval/JSON.parse), which is overkill in my mind, it's short enough to not require a utility function and maintains other truthey/falsey conventions.

var value = "false";
var result = (value == "false") != Boolean(value);

// value = "true"  => result = true
// value = "false" => result = false
// value = true    => result = true
// value = false   => result = false
// value = null    => result = false
// value = []      => result = true
// etc..

answered 5 years ago Cliff Mayson #32

function parseBool(value) {
    if (typeof value === "boolean") return value;

    if (typeof value === "number") {
        return value === 1 ? true : value === 0 ? false : undefined;
    }

    if (typeof value != "string") return undefined;

    return value.toLowerCase() === 'true' ? true : false;
}

answered 5 years ago CMCDragonkai #33

I wrote a function to match PHP's filter_var which does this nicely. Available in a gist: https://gist.github.com/CMCDragonkai/7389368

/**
 * Parses mixed type values into booleans. This is the same function as filter_var in PHP using boolean validation
 * @param  {Mixed}        value 
 * @param  {Boolean}      nullOnFailure = false
 * @return {Boolean|Null}
 */
var parseBooleanStyle = function(value, nullOnFailure = false){
    switch(value){
        case true:
        case 'true':
        case 1:
        case '1':
        case 'on':
        case 'yes':
            value = true;
            break;
        case false:
        case 'false':
        case 0:
        case '0':
        case 'off':
        case 'no':
            value = false;
            break;
        default:
            if(nullOnFailure){
                value = null;
            }else{
                value = false;
            }
            break;
    }
    return value;
};

answered 5 years ago Jan Remunda #34

Universal solution with JSON parse:

function getBool(val) {
    return !!JSON.parse(String(val).toLowerCase());
}

getBool("1"); //true
getBool("0"); //false
getBool("true"); //true
getBool("false"); //false
getBool("TRUE"); //true
getBool("FALSE"); //false

UPDATE (without JSON):

function getBool(val){ 
    var num = +val;
    return !isNaN(num) ? !!num : !!String(val).toLowerCase().replace(!!0,'');
}

I also created fiddle to test it http://jsfiddle.net/remunda/2GRhG/

answered 5 years ago Kyle Falconer #35

A lot of the existing answers are similar, but most ignore the fact that the given argument could also be an object.

Here is something I just whipped up:

Utils.parseBoolean = function(val){
    if (typeof val === 'string' || val instanceof String){
        return /true/i.test(val);
    } else if (typeof val === 'boolean' || val instanceof Boolean){
        return new Boolean(val).valueOf();
    } else if (typeof val === 'number' || val instanceof Number){
        return new Number(val).valueOf() !== 0;
    }
    return false;
};

...and the unit test for it

Utils.Tests = function(){
    window.console.log('running unit tests');

    var booleanTests = [
        ['true', true],
        ['false', false],
        ['True', true],
        ['False', false],
        [, false],
        [true, true],
        [false, false],
        ['gibberish', false],
        [0, false],
        [1, true]
    ];

    for (var i = 0; i < booleanTests.length; i++){
        var lhs = Utils.parseBoolean(booleanTests[i][0]);
        var rhs = booleanTests[i][1];
        var result = lhs === rhs;

        if (result){
            console.log('Utils.parseBoolean('+booleanTests[i][0]+') === '+booleanTests[i][1]+'\t : \tpass');
        } else {
            console.log('Utils.parseBoolean('+booleanTests[i][0]+') === '+booleanTests[i][1]+'\t : \tfail');
        }
    }
};

answered 5 years ago BrDaHa #36

I thought that @Steven 's answer was the best one, and took care of a lot more cases than if the incoming value was just a string. I wanted to extend it a bit and offer the following:

function isTrue(value){
    if (typeof(value) === 'string'){
        value = value.trim().toLowerCase();
    }
    switch(value){
        case true:
        case "true":
        case 1:
        case "1":
        case "on":
        case "yes":
            return true;
        default: 
            return false;
    }
}

It's not necessary to cover all the false cases if you already know all of the true cases you'd have to account for. You can pass anything into this method that could pass for a true value (or add others, it's pretty straightforward), and everything else would be considered false

answered 5 years ago Stefan Steiger #37

Wood-eye be careful. After seeing the consequences after applying the the top answer with 500+ upvotes, I feel obligated to post something that is actually useful:

Let's start with the shortest, but very strict way:

var str = "true";
var mybool = JSON.parse(str);

And end with a proper, more tolerant way:

var parseBool = function(str) 
{
    // console.log(typeof str);
    // strict: JSON.parse(str)

    if(str == null)
        return false;

    if (typeof str === 'boolean')
    {
        return (str === true);
    } 

    if(typeof str === 'string')
    {
        if(str == "")
            return false;

        str = str.replace(/^\s+|\s+$/g, '');
        if(str.toLowerCase() == 'true' || str.toLowerCase() == 'yes')
            return true;

        str = str.replace(/,/g, '.');
        str = str.replace(/^\s*\-\s*/g, '-');
    }

    // var isNum = string.match(/^[0-9]+$/) != null;
    // var isNum = /^\d+$/.test(str);
    if(!isNaN(str))
        return (parseFloat(str) != 0);

    return false;
}

Testing:

var array_1 = new Array(true, 1, "1",-1, "-1", " - 1", "true", "TrUe", "  true  ", "  TrUe", 1/0, "1.5", "1,5", 1.5, 5, -3, -0.1, 0.1, " - 0.1", Infinity, "Infinity", -Infinity, "-Infinity"," - Infinity", " yEs");

var array_2 = new Array(null, "", false, "false", "   false   ", " f alse", "FaLsE", 0, "00", "1/0", 0.0, "0.0", "0,0", "100a", "1 00", " 0 ", 0.0, "0.0", -0.0, "-0.0", " -1a ", "abc");


for(var i =0; i < array_1.length;++i){ console.log("array_1["+i+"] ("+array_1[i]+"): " + parseBool(array_1[i]));}

for(var i =0; i < array_2.length;++i){ console.log("array_2["+i+"] ("+array_2[i]+"): " + parseBool(array_2[i]));}

for(var i =0; i < array_1.length;++i){ console.log(parseBool(array_1[i]));}
for(var i =0; i < array_2.length;++i){ console.log(parseBool(array_2[i]));}

answered 5 years ago user3310384 #38

A shorter way to write this, could be var isTrueSet = (myValue === "true") ? true : false; Presuming only "true" is true and other values are false.

answered 4 years ago Mahes #39

Simple solution i have been using it for a while

function asBoolean(value) {

    return (''+value) === 'true'; 

}


// asBoolean(true) ==> true
// asBoolean(false) ==> false
// asBoolean('true') ==> true
// asBoolean('false') ==> false

answered 4 years ago Prestaul #40

var falsy = /^(?:f(?:alse)?|no?|0+)$/i;
Boolean.parse = function(val) { 
    return !falsy.test(val) && !!val;
};

This returns false for every falsy value and true for every truthy value except for 'false', 'f', 'no', 'n', and '0' (case-insensitive).

// False
Boolean.parse(false);
Boolean.parse('false');
Boolean.parse('False');
Boolean.parse('FALSE');
Boolean.parse('f');
Boolean.parse('F');
Boolean.parse('no');
Boolean.parse('No');
Boolean.parse('NO');
Boolean.parse('n');
Boolean.parse('N');
Boolean.parse('0');
Boolean.parse('');
Boolean.parse(0);
Boolean.parse(null);
Boolean.parse(undefined);
Boolean.parse(NaN);
Boolean.parse();

//True
Boolean.parse(true);
Boolean.parse('true');
Boolean.parse('True');
Boolean.parse('t');
Boolean.parse('yes');
Boolean.parse('YES');
Boolean.parse('y');
Boolean.parse('1');
Boolean.parse('foo');
Boolean.parse({});
Boolean.parse(1);
Boolean.parse(-1);
Boolean.parse(new Date());

answered 4 years ago konsumer #41

I do this, which will handle 1=TRUE=yes=YES=true, 0=FALSE=no=NO=false:

BOOL=false
if (STRING)
  BOOL=JSON.parse(STRING.toLowerCase().replace('no','false').replace('yes','true'));

Replace STRING with the name of your string variable.

If it's not null, a numerical value or one of these strings: "true", "TRUE", "false", "FALSE", "yes", "YES", "no", "NO" It will throw an error (intentionally.)

answered 4 years ago Timo #42

I use an own method which includes a check if the object exists first and a more intuitive conversion to boolean:

function str2bool(strvalue){
  return (strvalue && typeof strvalue == 'string') ? (strvalue.toLowerCase() == 'true' || strvalue == '1') : (strvalue == true);
}

The results are:

var test; // false
var test2 = null; // false
var test3 = 'undefined'; // false
var test4 = 'true'; // true
var test5 = 'false'; // false
var test6 = true; // true
var test7 = false; // false
var test8 = 1; // true
var test9 = 0; // false
var test10 = '1'; // true
var test11 = '0'; // false

Fiddle: http://jsfiddle.net/av5xcj6s/

answered 4 years ago pie6k #43

I'm using this one

String.prototype.maybeBool = function(){

    if ( ["yes", "true", "1", "on"].indexOf( this.toLowerCase() ) !== -1 ) return true;
    if ( ["no", "false", "0", "off"].indexOf( this.toLowerCase() ) !== -1 ) return false;

    return this;

}

"on".maybeBool(); //returns true;
"off".maybeBool(); //returns false;
"I like js".maybeBool(); //returns "I like js"

answered 4 years ago sospedra #44

There are a lot of answers and it's hard to pick one. In my case, I prioritise the performance when choosing, so I create this jsPerf that I hope can throw some light here.

Brief of results (the higher the better):

  1. Conditional statement: 2,826,922
  2. Switch case on Bool object: 2,825,469
  3. Casting to JSON: 1,867,774
  4. !! conversions: 805,322
  5. Prototype of String: 713,637

They are linked to the related answer where you can find more information (pros and cons) about each one; specially in the comments.

answered 4 years ago Martin Malinda #45

To evaluate both boolean and boolean-like strings like boolean I used this easy formula:

var trueOrStringTrue = (trueOrStringTrue === true) || (trueOrStringTrue === 'true');

As is apparent, it will return true for both true and 'true'. Everything else returns false.

answered 4 years ago Fizer Khan #46

To convert both string("true", "false") and boolean to boolean

('' + flag) === "true"

Where flag can be

 var flag = true
 var flag = "true"
 var flag = false
 var flag = "false"

answered 3 years ago sputn1k #47

works perfectly and very simple:

var boolean = "false";
boolean = (boolean === "true");

//boolean = JSON.parse(boolean); //or this way.. 

to test it:

var boolean = "false";
boolean = (boolean === "true");

//boolean = JSON.parse(boolean); //or this way.. 

if(boolean == true){
    alert("boolean = "+boolean);
}else{
    alert("boolean = "+boolean);
}

answered 3 years ago vbranden #48

another solution. jsFiddle

var toBoolean = function(value) {
    var strValue = String(value).toLowerCase();
    strValue = ((!isNaN(strValue) && strValue !== '0') &&
        strValue !== '' &&
        strValue !== 'null' &&
        strValue !== 'undefined') ? '1' : strValue;
    return strValue === 'true' || strValue === '1' ? true : false
};

test cases run in node

> toBoolean(true)
true
> toBoolean(false)
false
> toBoolean(undefined)
false
> toBoolean(null)
false
> toBoolean('true')
true
> toBoolean('True')
true
> toBoolean('False')
false
> toBoolean('false')
false
> toBoolean('0')
false
> toBoolean('1')
true
> toBoolean('100')
true
> 

answered 3 years ago Eugene Tiurin #49

The fastest safe way to convert a string to a boolean in one line of code

One of features that help to fasten the code execution in Javascript is Short-Circuit Evaluation:

As logical expressions are evaluated left to right, they are tested for possible "short-circuit" evaluation using the following rules:

  • false && (anything) is short-circuit evaluated to false.
  • true || (anything) is short-circuit evaluated to true.

So that if you want to test a string value for being true of false in JSON.parse way of test and keep the performance strong, you may use the || operator to exclude the slow code from execution in case the test value is of boolean type.

test === true || ['true','yes','1'].indexOf(test.toString().toLowerCase()) > -1

As the Array.prototype.indexOf() method is a part of ECMA-262 standard in the 5th edition, you may need a polyfill for the old browsers support.

// Production steps of ECMA-262, Edition 5, 15.4.4.14
// Reference: http://es5.github.io/#x15.4.4.14
if (!Array.prototype.indexOf) {
  Array.prototype.indexOf = function(searchElement, fromIndex) {

    var k;

    // 1. Let O be the result of calling ToObject passing
    //    the this value as the argument.
    if (this == null) {
      throw new TypeError('"this" is null or not defined');
    }

    var O = Object(this);

    // 2. Let lenValue be the result of calling the Get
    //    internal method of O with the argument "length".
    // 3. Let len be ToUint32(lenValue).
    var len = O.length >>> 0;

    // 4. If len is 0, return -1.
    if (len === 0) {
      return -1;
    }

    // 5. If argument fromIndex was passed let n be
    //    ToInteger(fromIndex); else let n be 0.
    var n = +fromIndex || 0;

    if (Math.abs(n) === Infinity) {
      n = 0;
    }

    // 6. If n >= len, return -1.
    if (n >= len) {
      return -1;
    }

    // 7. If n >= 0, then Let k be n.
    // 8. Else, n<0, Let k be len - abs(n).
    //    If k is less than 0, then let k be 0.
    k = Math.max(n >= 0 ? n : len - Math.abs(n), 0);

    // 9. Repeat, while k < len
    while (k < len) {
      // a. Let Pk be ToString(k).
      //   This is implicit for LHS operands of the in operator
      // b. Let kPresent be the result of calling the
      //    HasProperty internal method of O with argument Pk.
      //   This step can be combined with c
      // c. If kPresent is true, then
      //    i.  Let elementK be the result of calling the Get
      //        internal method of O with the argument ToString(k).
      //   ii.  Let same be the result of applying the
      //        Strict Equality Comparison Algorithm to
      //        searchElement and elementK.
      //  iii.  If same is true, return k.
      if (k in O && O[k] === searchElement) {
        return k;
      }
      k++;
    }
    return -1;
  };
}

answered 3 years ago Siten #50

To Get Boolean values from string or number Here is good solution:

var boolValue = Boolean(Number('0'));

var boolValue = Boolean(Number('1'));

First will return false and second will return true.

answered 3 years ago ecabuk #51

function isTrue(val) {
    try {
        return !!JSON.parse(val);
    } catch (e) {
        return false;
    }
}

answered 3 years ago jdnichollsc #52

Take care, maybe in the future the code change and return boolean instead of one string at the moment.

The solution would be:

//Currently
var isTrue = 'true';
//In the future (Other developer change the code)
var isTrue = true;
//The solution to both cases
(isTrue).toString() == 'true'

answered 2 years ago benipsen #53

Lots of fancy answers here. Really surprised no one has posted this solution:

var booleanVal = toCast > '';

This resolves to true in most cases other than bool false, number zero and empty string (obviously). You can easily look for other falsey string values after the fact e.g.:

var booleanVal = toCast > '' && toCast != 'false' && toCast != '0';  

answered 2 years ago Frederico Kronemberger Da Cruz #54

Boolean(Number(value));
var value = 1;  //true
var value = "1" //true
var value = 0;  //false
var value = "0" //false`

answered 2 years ago Sandip Nirmal #55

There are already so many answers available. But following can be useful in some scenarios.

// One can specify all values against which you consider truthy
var TRUTHY_VALUES = [true, 'true', 1];

function getBoolean(a) {
    return TRUTHY_VALUES.some(function(t) {
        return t === a;
    });
}

This can be useful where one examples with non-boolean values.

getBoolean('aa'); // false
getBoolean(false); //false
getBoolean('false'); //false

getBoolean('true'); // true
getBoolean(true); // true
getBoolean(1); // true

answered 2 years ago Hakam Fostok #56

This has been taken from the accepted answer, but really it has a very weak point, and I am shocked how it got that count of upvotes, the problem with it that you have to consider the case of the string because this is case sensitive

var isTrueSet = (myValue.toLowerCase() === 'true');

answered 2 years ago jose.serapicos #57

I use this simple approach (using "myVarToTest"):

var trueValuesRange = ['1', 1, 'true', true];

myVarToTest = (trueValuesRange.indexOf(myVarToTest) >= 0);

answered 2 years ago Roman Masyhar #58

Take it easy using this lib.

https://github.com/rohmanhm/force-boolean

you just need to write a single line

const ForceBoolean = require('force-boolean')

const YOUR_VAR = 'false'
console.log(ForceBoolean(YOUR_VAR)) // it's return boolean false

It's also support for following

 return false if value is number 0
 return false if value is string '0'
 return false if value is string 'false'
 return false if value is boolean false
 return true if value is number 1
 return true if value is string '1'
 return true if value is string 'true'
 return true if value is boolean true

answered 2 years ago Steve Mc #59

var trueVals = ["y", "t", "yes", "true", "gimme"];
var isTrueSet = (trueVals.indexOf(myValue) > -1) ? true : false;

or even just

var trueVals = ["y", "t", "yes", "true", "gimme"];
var isTrueSet = (trueVals.indexOf(myValue) > -1);

Similar to some of the switch statements but more compact. The value returned will only be true if the string is one of the trueVals strings. Everything else is false. Of course, you might want to normalise the input string to make it lower case and trim any spaces.

answered 2 years ago Surya R Praveen #60

Convert String to Boolean

var vIn = "true";
var vOut = vIn.toLowerCase()=="true"?1:0;

Convert String to Number

var vIn = 0;
var vOut = parseInt(vIn,10/*base*/);

answered 1 year ago Dayem Siddiqui #61

Here is simple function that will do the trick,

   function convertStringToBool(str){
        return ((str === "True") || (str === "true")) ? true:false;
    }

This will give the following result

convertStringToBool("false") //returns false
convertStringToBool("true") // returns true
convertStringToBool("False") // returns false
convertStringToBool("True") // returns true

answered 1 year ago Vitim.us #62

One Liner

We just need to account for the "false" string since any other string (including "true") is already true.

function b(v){ return v==="false" ? false : !!v; }

Test

b(true)    //true
b('true')  //true
b(false)   //false
b('false') //false

A more exaustive version

function bool(v){ return v==="false" || v==="null" || v==="NaN" || v==="undefined" || v==="0" ? false : !!v; }

Test

bool(true)        //true
bool("true")      //true
bool(1)           //true
bool("1")         //true
bool("hello")     //true

bool(false)       //false
bool("false")     //false
bool(0)           //false
bool("0")         //false
bool(null)        //false
bool("null")      //false
bool(NaN)         //false
bool("NaN")       //false
bool(undefined)   //false
bool("undefined") //false
bool("")          //false

bool([])          //true
bool({})          //true
bool(alert)       //true
bool(window)      //true

answered 1 year ago Chanakya Vadla #63

String(true).toLowerCase() == 'true'; // true
String("true").toLowerCase() == 'true'; // true
String("True").toLowerCase() == 'true'; // true
String("TRUE").toLowerCase() == 'true'; // true

String(false).toLowerCase() == 'true'; // false

If you are not sure of the input, the above works for boolean and as well any string.

answered 1 year ago guest271314 #64

You can use Function to return a Boolean value from string "true" or "false"

const TRUE_OR_FALSE = str => new Function(`return ${str}`)();

const [TRUE, FALSE] = ["true", "false"];

const [T, F] = [TRUE_OR_FALSE(TRUE), TRUE_OR_FALSE(FALSE)];

console.log(T, typeof T); // `true` `"boolean"`

console.log(F, typeof F); // `false` `"boolean"`

answered 1 year ago Mohammad Farahani #65

you can use :

 var    trueOrFalse='True';
    result =JSON.parse(trueOrFalse.toLowerCase());
    if(result==true)
      alert('this is ture');
    else 
     ('this is false');

in this case the .toLowerCase is important

answered 1 year ago danday74 #66

The `toBoolean' function returns false for null, undefined, '', 'false'. It returns true for any other string:

const toBoolean = (bool) => {
  if (bool === 'false') bool = false
  return !!bool
}

toBoolean('false') // returns false

answered 12 months ago Kostanos #67

I'm using this one when I get value from URL/Form or other source.

It is pretty universal one line piece of code.

Maybe not the best for performance, if you need to run it millions times let me know, we can check how to optimize it, otherwise is pretty good and customizable.

boolResult = !(['false', '0', '', 'undefined'].indexOf(String(myVar).toLowerCase().trim()) + 1);

Result:

myVar = true;  // true
myVar = 'true';  // true
myVar = 'TRUE';  // true
myVar = '1';  // true
myVar = 'any other value not related to false';  // true

myVar = false; // false
myVar = 'false';  // false
myVar = 'FALSE';  // false
myVar = '0';  // false

answered 11 months ago OhkaBaka #68

Holy god some of these answers are just wild. I love JS and its infinite number of ways to skin a bool.

My preference, which I was shocked not to see already, is:

testVar = testVar.toString().match(/^(true|[1-9][0-9]*|[0-9]*[1-9]+|yes)$/i) ? true : false;

answered 10 months ago Yohan #69

why don't you try something like this

Boolean(JSON.parse((yourString.toString()).toLowerCase()));

It will return an error when some other text is given rather than true or false regardless of the case and it will capture the numbers also as

// 0-> false
// any other number -> true

answered 8 months ago pankaj sharma #70

This function can handle string as well as Boolean true/false.

function stringToBoolean(val){
    var a = {
        'true':true,
        'false':false
    };
    return a[val];
}

Demonstration below:

function stringToBoolean(val) {
  var a = {
    'true': true,
    'false': false
  };
  return a[val];
}

console.log(stringToBoolean("true"));

console.log(typeof(stringToBoolean("true")));

console.log(stringToBoolean("false"));

console.log(typeof(stringToBoolean("false")));

console.log(stringToBoolean(true));

console.log(typeof(stringToBoolean(true)));

console.log(stringToBoolean(false));

console.log(typeof(stringToBoolean(false)));

console.log("=============================================");
// what if value was undefined? 
console.log("undefined result:  " + stringToBoolean(undefined));
console.log("type of undefined result:  " + typeof(stringToBoolean(undefined)));
console.log("=============================================");
// what if value was an unrelated string?
console.log("unrelated string result:  " + stringToBoolean("hello world"));
console.log("type of unrelated string result:  " + typeof(stringToBoolean(undefined)));

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