JavaScript Let - What is Let in JavaScript
JavaScript Let
- The let keyword was introduced in ES6 (2015).
- Variables defined with let cannot be redeclared.
- Variables defined with let must be declared before use.
- Variables defined with let have Block Scope.
Cannot be Redeclared
- Variables defined with let cannot be redeclared.
- You cannot accidentally redeclare a variable.
- With let you can not do this.
let x = "John Doe";
let x = 0;
// SyntaxError: 'x' has already been declared
Block Scope
- Before ES6 (2015), JavaScript had only Global Scope and Function Scope.
- ES6 introduced two important new JavaScript keywords: let and const.
- These two keywords provide Block Scope in JavaScript.
- Variables declared inside a { } block cannot be accessed from outside the block:
{
let x = 2;
}
// x can NOT be used here
Redeclaring Variables let
- Redeclaring a variable using the let keyword can solve this problem.
- Redeclaring a variable inside a block will not redeclare the variable outside the block.
Sample Code
<!DOCTYPE html>
<html>
<body>
<h2>Redeclaring a Variable Using let</h2>
<p id="demo"></p>
<script>
let x = 10;
// Here x is 10
{
let x = 2;
// Here x is 2
}
// Here x is 10
document.getElementById("demo").innerHTML = x;
</script>
</body>
</html>
Output
Redeclaring a Variable Using let
10