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How to declare boolean variables in JavaScript?
A boolean variable in JavaScript has two values: true or false. Boolean values are essential for conditional logic, comparisons, and control flow in JavaScript applications.
Syntax
let variableName = true; // or false let variableName = Boolean(value); // converts value to boolean
Direct Boolean Assignment
The simplest way to declare boolean variables is by directly assigning true or false:
<!DOCTYPE html>
<html>
<body>
<p>Boolean variable examples:</p>
<button onclick="showBooleans()">Show Boolean Values</button>
<p id="result"></p>
<script>
function showBooleans() {
let isActive = true;
let isComplete = false;
document.getElementById("result").innerHTML =
"isActive: " + isActive + "<br>" +
"isComplete: " + isComplete;
}
</script>
</body>
</html>
Boolean from Comparisons
Boolean values are often created through comparison operations:
<!DOCTYPE html>
<html>
<body>
<p>35 > 20</p>
<button onclick="myValue()">Click for result</button>
<p id="test"></p>
<script>
function myValue() {
let result = 35 > 20;
document.getElementById("test").innerHTML =
"Result: " + result + " (type: " + typeof result + ")";
}
</script>
</body>
</html>
Using Boolean() Constructor
The Boolean() function converts other values to boolean:
<!DOCTYPE html>
<html>
<body>
<button onclick="testBoolean()">Test Boolean Conversion</button>
<p id="conversion"></p>
<script>
function testBoolean() {
let results = [
"Boolean(1): " + Boolean(1),
"Boolean(0): " + Boolean(0),
"Boolean('hello'): " + Boolean('hello'),
"Boolean(''): " + Boolean(''),
"Boolean(null): " + Boolean(null)
];
document.getElementById("conversion").innerHTML = results.join("<br>");
}
</script>
</body>
</html>
Falsy and Truthy Values
| Falsy Values | Truthy Values |
|---|---|
false, 0, "", null, undefined, NaN
|
Everything else (non-empty strings, non-zero numbers, objects, arrays) |
Conclusion
Boolean variables are declared using true/false literals, comparison operations, or the Boolean() constructor. Understanding truthy and falsy values is crucial for effective boolean usage in JavaScript.
Updated on: 2026-03-15T21:26:20+05:30
703 Views
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