How To Convert a string to a boolean in JavaScript – Definitive Guide?

Several ways are available to convert a string to a boolean, depending on how we want the conversion.

You can convert a String to a boolean in Javascript using the var isBoolean=Boolean(str) statement.

Basic Example

    var str='true';

    var isBoolean= (str === 'true'); 

    console.log(typeof isBoolean); 

When working with HTML elements, few elements only deal with boolean type values, and you may have string data to process.

This tutorial teaches you the different methods to convert a string to a boolean in JavaScript and when it is appropriate to use them.

Using String Comparison

The easiest way to convert a string value to a boolean value is by comparing the string value with ‘true’.

Code

var str='true';
var isBoolean= (str === 'true'); 
console.log("Value of isBoolean: "+ isBoolean); 
console.log("Type of isBoolean: "+ typeof isBoolean); 

This method is case-sensitive. In this approach, you will be doing an exact match of string comparison.

Output

    Value of isBoolean:  true

    Type of isBoolean: boolean

The string variable(str) is compared against the string value true, and it returns true if it matches exactly.

Code

Now let us see another example. Here the variable str holds value True.

    var str='True';

    var isBoolean= (str === 'true'); 

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean); 

Since True and true are in a different cases, the comparison returns false.

Output

    Value of isBoolean: false

    Type of isBoolean: boolean

To compare in a case-insensitive way,

• Convert the string value to equivalent javascript letter casing before comparing it with a conditional string value.

Code

    var str='True';

    var isBoolean= (str.toLowerCase() === 'true'); 

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

Output

The output will be true because both the strings are in the same case.

    Value of isBoolean: true

    Type of isBoolean: boolean

Using toLowerCase() for comparison will throw an error if the string is undefined or null.

If a condition check fails in a string comparison, it will return false.

Code

    var str='jsowl';

    var isBoolean=(str === 'true');

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

Output

    Value of isBoolean: false

    Type of isBoolean: boolean

This is how you can use the string comparison approach to convert string to boolean.

Using Boolean Constructor

In this approach,

• Pass the string value to the Boolean constructor,
• It will return a boolean value.

Code

    const str = 'false';

    var isBoolean=Boolean(str);  

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

Output

Value of isBoolean: true
Type of isBoolean: boolean

Converting any string using the Boolean constructor approach will return true except the Falsy Values.

Falsy Values
Javascript has 6 falsy values, and converting these values to boolean will always return false.

Below are the 6 falsy values

1. null 
2.  0
3.  false
4. NaN 
5. undefined
6. "" - (empty string)

Example

    Boolean(null); // false 

    Boolean(0); // false 

    Boolean(false); // false 

    Boolean(NaN); // false 

    Boolean(undefined); // false 

    Boolean(""); // false

Converting string to boolean using the new Boolean constructor approach is not recommended because it comes with certain disadvantages, as listed below,

It is preferred to use primitive types over object types because the new Boolean will return an object type instead of a boolean.

• Primitive types are immutable, making it cheaper to share references. It will be just ‘true’ or ‘false’.

Code

    var str = 'str';
    // Not recommended
    typeof new Boolean(str); // returns object  
    // Preferred 
    typeof Boolean(str); // returns boolean

Using Double Not Syntax

Double Not Syntax works similarly to the Boolean constructor.

The only difference is, it is easy to use because of its simple syntax, but most developers would easily remember Boolean constructors better.

Code

    var str='True';

    var isBoolean=!!(str);  

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

Output

    Value of isBoolean: true

    Type of isBoolean: boolean

First, Not(!) will compel the value of the boolean and inverse it. Anything will be false now, So to reverse the value to true, add one more Not(!) and put it together as !!.

    var str = 'True';

    // Single Not
    !str; //false

    // Double Not      
    !!str; // true

Using JSON.parse()

You can use JSON (built-in javascript object) and use the parse method of JSON to convert string to boolean (either true/false).

Code

    var str='True';

    var isBoolean=JSON.parse(str.toLowerCase()); 

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

Output

    Value of isBoolean: true
    Type of isBoolean: boolean

Using JSON.parse() to convert string to boolean, you can only pass ‘ true/false’ as string values, and anything other than ‘true/false’ will throw an error JSON syntax error.

Code

    var str='True';

    var isBoolean=JSON.parse(str); 

Output:

    "Uncaught SyntaxError: Unexpected token T in JSON at position 0."

Using Regex()

You can also use a simple regular expression to validate a string based on a specific condition;

• If this particular condition met, it returns true
• Else false.

Code

    var str='true';

    var isBoolean=(/true/i).test(stringValue);  

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

Output

    Value of isBoolean: true

    Type of isBoolean: boolean

Using switch-case

Switch-case conversion can be used in places where multiple selective conditions need to be handled to determine a boolean value.

Code

    var str='true';

    var isBoolean=getBooleanUsingSwitchCase(str); 

    console.log("Value of isBoolean: "+ isBoolean); 

    console.log("Type of isBoolean: "+ typeof isBoolean);

    function getBooleanUsingSwitchCase(value){ 

        switch(value) { 
            case true: 
            case "true": 
            case 1: 
            case "1": 
            case "on": 
            case "yes": 
                return true; 
            default: 
                return false; 
        }

    }

Output

    Value of isBoolean: true
    Type of isBoolean: boolean

In the above example, all the input values with either of the conditional values(true/”true”/1/”1″/” on “/”yes” ) will return a boolean value as true, and in other cases, it will return a boolean false.

Using the ternary operator

This is a simple conditional check to determine the return value(true/false).

Code

    var str= "true";
    let isBoolean= str.toLowerCase() == 'true' ? true : false;
    console.log("Value of isBoolean: "+ isBoolean); 
    console.log("Type of isBoolean: "+ typeof isBoolean);

Output:

    Value of isBoolean: true
    Type of isBoolean: boolean

JSfiddle

This tutorial is available in this JSFiddle.

Additional Resources

• How to Convert Javascript Object to JSON string?
• How To Check If String Contains A Substring In Javascript?
• How To Replace All Occurrences Of A String In JavaScript?
• How To Remove A Text From A String In JavaScript?
• How To Convert a String into a Character Array in JavaScript