How can I convert a string to boolean in JavaScript?

Question

Do:

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

using the identity operator (===), which doesn't make any implicit type conversions when the compared variables have different types.

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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.

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".

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

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Original answer:

How about?

JSON.parse("True".toLowerCase());

or with jQuery

$.parseJSON("TRUE".toLowerCase());

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);
    }
}

I think this is much universal:

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

It goes:

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