JavaScript How to Convert String to Boolean Easily

To convert a string to boolean in JavaScript, compare the string to a truthy value like const bool = (str === 'true') which returns true if the string is exactly 'true', otherwise false.

Examples

Input'true'

Outputtrue

Input'false'

Outputfalse

Input'hello'

Outputfalse

How to Think About It

To convert a string to a boolean, think about what strings should mean true or false. Usually, the string 'true' means true and anything else means false. So you check if the string equals 'true' exactly, then return true; otherwise, return false.

Algorithm

1

Get the input string.

2

Check if the string is exactly equal to 'true'.

3

If yes, return true.

4

Otherwise, return false.

Code

javascript

const strToBool = (str) => str === 'true';

console.log(strToBool('true'));  // true
console.log(strToBool('false')); // false
console.log(strToBool('hello')); // false

Output

true
false
false

Dry Run

Let's trace the input 'true' through the code

1

Input string

str = 'true'

2

Compare string

'true' === 'true' is true

3

Return result

Returns true

Input String	Comparison Result	Returned Boolean
'true'	true	true
'false'	false	false
'hello'	false	false

Why This Works

Step 1: Exact match check

Using === checks if the string is exactly 'true', so only that string returns true.

Step 2: Boolean result

The comparison returns a boolean value directly, so no extra conversion is needed.

Step 3: Simple and clear

This method is simple and avoids confusion from other string values.

Alternative Approaches

Using JSON.parse

javascript

const strToBool = (str) => {
  try {
    return JSON.parse(str.toLowerCase());
  } catch {
    return false;
  }
};

console.log(strToBool('true'));  // true
console.log(strToBool('false')); // false
console.log(strToBool('hello')); // false

This parses 'true' and 'false' strings but throws error for others, so we catch and return false.

Using a set of truthy strings

javascript

const truthyStrings = new Set(['true', 'yes', '1']);
const strToBool = (str) => truthyStrings.has(str.toLowerCase());

console.log(strToBool('true'));  // true
console.log(strToBool('yes'));   // true
console.log(strToBool('no'));    // false

Allows more flexible true values but requires defining which strings count as true.

Complexity: O(1) time, O(1) space

Time Complexity

The comparison str === 'true' runs in constant time because it only checks fixed-length strings.

Space Complexity

No extra memory is used besides the input string and a boolean return value, so space is constant.

Which Approach is Fastest?

The direct equality check is fastest and simplest. JSON.parse adds overhead and error handling. Using a set is flexible but uses more memory.

Approach	Time	Space	Best For
Direct equality (str === 'true')	O(1)	O(1)	Simple exact match
JSON.parse with try/catch	O(1)	O(1)	Parsing JSON boolean strings
Set of truthy strings	O(1)	O(n) for set size	Flexible true values