Javascript Variables - How to declare variables in different ways in JavaScript ?
Javascript Variables
- 4 Ways to Declare a JavaScript Variable
- Using var
- Using let
- Using const
- Using nothing
What are Variables
- Variables are containers for storing data (storing data values).
Var Keyword
In this example, a, b, and c, are variables, declared with the var keyword.
Sample Code
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Variables</h1>
<p>In this example, a, b, and c are variables.</p>
<p id="demo"></p>
<script>
var a = 4;
var b = 10;
var c = a + b;
document.getElementById("demo").innerHTML = "The value of c is: " + c;
</script>
</body>
</html>Output
JavaScript Variable
In this example, a, b, and c are variables.
The value of c is: 14let Keyword
In this example, x, y, and z, are variables, declared with the let keyword.
<!DOCTYPE html>
<html>
<body>
<h2>JavaScript Variables</h2>
<p>In this example, x, y, and z are variables.</p>
<p id="demo"></p>
<script>
let x = 5;
let y = 6;
let z = x + y;
document.getElementById("demo").innerHTML = "The value of z is: " + z;
</script>
</body>
</html>
Output
JavaScript Variables
In this example, x, y, and z are variables.
The value of z is: 11
In this example, x, y, and z, are undeclared variables.
Sample Code
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Variables</h1>
<p>In this example, x, y, and z are undeclared variables.</p>
<p id="demo"></p>
<script>
x = 5;
y = 6;
z = x + y;
document.getElementById("demo").innerHTML = "The value of z is: " + z;
</script>
</body>
</html>Output
JavaScript Variables
In this example, x, y, and z are undeclared variables.
The value of z is: 11When to Use JavaScript var ?
- Always declare JavaScript variables with var,let, or const.
- The var keyword is used in all JavaScript code from 1995 to 2015.
- The let and const keywords were added to JavaScript in 2015.
- If you want your code to run in older browsers, you must use var.
When to Use JavaScript const ?
- If you want a general rule: always declare variables with const.
- If you think the value of the variable can change, use let.
- In this example, p1, p2, and total, are variables:
Const Keyword
Sample Code
<!DOCTYPE html>
<html>
<body>
<h1>JavaScript Variables</h1>
<p>In this example, p1, p2, and total are variables.</p>
<p id="demo"></p>
<script>
const p1 = 5;
const p2 = 6;
let total = p1 + p2;
document.getElementById("demo").innerHTML = "The total is: " + total;
</script>
</body>
</html>Output
JavaScript Variables
In this example, p1, p2, and total are variables.
The total is: 11