Use var or let or const keyword to create Boolean variable in JavaScript. A boolean variable is used to identify whether a condition is true or false.
Accordingly, boolean values can only assume two values:
truefalse
let exampleBoolean = true;
let anotherExample = false;Note: Never create a boolean using the Boolean constructor function. Instead, just use the literal values, true or false.
JavaScript Boolean variable
Simple example code.
<!DOCTYPE html>
<html>
<body>
<script>
var age = 0;
// bad
var hasAge = new Boolean(age);
console.log(hasAge)
// good
var hasAge = Boolean(age);
console.log(hasAge)
// good
var hasAge = !!age;
console.log(hasAge)
// good
var hasAge = !age;
console.log(hasAge)
</script>
</body>
</html>Output:
More Code
// falsy values: false, 0, -0, 0n, null, undefined, NaN, and the empty string ""
console.log(Boolean(false)) // false
console.log(Boolean(0)) // false
console.log(Boolean(-0)) // false
console.log(Boolean(0n)) // false
console.log(Boolean(null)) // false
console.log(Boolean(undefined)) // false
console.log(Boolean(NaN)) // false
console.log(Boolean("")) // false
console.log(typeof Boolean("")) // boolean
// truthy values: true, 1, -1, 1n, -1n, Infinity, -Infinity, " ", {}, []
console.log(Boolean(true)) // true
console.log(Boolean(1)) // true
console.log(Boolean(-1)) // true
console.log(Boolean(1n)) // true
console.log(Boolean(-1n)) // true
console.log(Boolean(Infinity)) // true
console.log(Boolean(-Infinity)) // true
console.log(Boolean(" ")) // true
console.log(Boolean({})) // true
console.log(Boolean([])) // true
console.log(typeof Boolean([])) // booleanHow to change a boolean value in JS?
Answer: To change a boolean to its opposite value you can use negation (!), for example x = !x means “set x to false if it’s truthy or to true if it’s falsy”.
<script>
let testBool = true;
console.log(testBool);
function toggle() {
testBool = !testBool;
console.log(testBool);
}
</script>Do comment if you have any doubts or suggestions on this JS variable topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version
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