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JAVASCRIPT BOOLEAN


The boolean in javascript is a primitive data type that has two values true representing yes and false representing no.

Boolean is generally used in conditional statements or at places when we have to control the flow example loops, if-else, switch, etc.

Example

// Boolean
var positive = true;
var negative = false;
console.log(typeof positive);
console.log(typeof negative);

//String
var x = "true";
var y = "false";
console.log(typeof x);
console.log(typeof y);
▶ Try it

Boolean Constructor Function

The Boolean() constructor function converts the value passed to it to a boolean value.

The Boolean() function can also convert javascript expressions to boolean values.

Example

var positive = Boolean(true);
var negative = Boolean(false);
console.log(typeof positive);
console.log(typeof negative);

var x = Boolean(10 > 20);
var y = Boolean(15 === 15);
var z = Boolean(20 < 30);
console.log(x, y, z);
▶ Try it

Note: If the value passed is 0, undefined, null, NaN, empty string, or false, the Boolean() function will return false and if the value passed is any other value, the Boolean() function will return true.

Let's see how the Boolean() function works with some examples.

Example

console.log("0 is " + Boolean(0));
console.log("1 is " + Boolean(1));
console.log("-15 is " + Boolean(-15));
console.log("1 < 2 is " + Boolean(1 < 2));
console.log("25 === 5*5 is " + Boolean(25 === 5*5));
console.log("Any valid string returns " + Boolean("Some string"));
console.log("Empty string is " + Boolean(''));
console.log("All object returns " + Boolean([]));
console.log("All object returns " + Boolean({}));
console.log("undefined is " + Boolean(undefined));
console.log("null is " + Boolean(null));
console.log("NaN is " + Boolean(NaN));
▶ Try it

Boolean as Object

Generally Boolean is a primitive data type when created using literals. Example var bool = true;.

But booleans can be made objects using new keywords. Example var boolObj = new Boolean(true);.

Example

var bool = true; // boolean
var boolObj = new Boolean(true); // object
console.log(typeof bool);
console.log(typeof boolObj);
▶ Try it

Note: Use literals to define boolean because boolean as the object is slow.


JavaScript String To Boolean

To convert a string to boolean, we can use the Boolean() function or you can use the negation operator !.

Negation (!) operator is used to convert a value to its opposite value. Example !true will return false and !false will return true.

To convert a string to boolean use negation operator it will convert it to boolean but opposite value so use another negation operator to convert it to its original value. Example !!'Hello world' will return true.

Example

var str1 = "Hello world";
var str2 = "";
// negation operator
console.log(!!str1);
console.log(!!str2);

// Boolean() function
console.log(Boolean(str1));
console.log(Boolean(str2));

Conclusion

Boolean is the truthy value of any type of data in javascript. It can be either true or false.

Booleans can be converted to string using Boolean() function or using negation operator !.


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