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JavaScript | Let
  • Last Updated : 27 Mar, 2019


let is a keyword used to declare variables in javascript that are block scoped. There are three ways you can declare variables in javascript let, const, var(old). ES6 or ES2015 defines new keywords to declare varaibles in javascript.

Syntax:

let x=1, y=3, z=4;

Block Scope:

A variable can be either of global or local scope. A global variable is a variable declared in the main body of the source code, outside all functions, while a local variable is one declared within the body of a function or a block.

Global Scope:



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let num=10;
console.log(num);
function fun(){
    console.log(num);
}
fun(); // calling the function

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Output:

Function Scope:

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function fun(){
    let num=10;
    console.log(num);
}
fun(); //  caling the function
console.log(num);

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Output:

Block Scope:

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{
    let x=23;
    console.log(x);
}
console.log(x);

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Output:

Redeclaring Variables in different blocks:

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let x=77;
{
    let x=23;
    console.log(x);
}
console.log(x);

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Output:

Redeclaring Variables in same blocks:

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let x=77;
{
    let x=23; // legal
    console.log(x);
}
let x=67;// illegal
console.log(x);

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Output:

Does not support Hoisting:

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x=12;
console.log(x);
let x;

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Output:

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