Everything You Need To Know About Let in Javascript

The let statement declares a block-scoped local variable, optionally initializing it to a value. It can be defined using let keyword.

        
let x =1;
console.log(x);     // Output : 1        
    

Variables defined with let cannot be redeclared.

        
let x = "John";
           
let x = 0;

// SyntaxError: 'x' has already been declared
        
    
let is block scoped

A block is a chunk of code bounded by {}. A block lives in curly braces. Anything within curly braces is a block.

So a variable declared in a block with let is only available for use within that block.

        
let str = 5;
            
if (str > 2) {
    let hello = "Hello World";
    console.log(hello);     //  Output : "Hello World"
}
console.log(hello)          // hello is not defined
        
    

We see that using hello outside its block (the curly braces where it was defined) returns an error. This is because let variables are block-scoped.we can see another example below

        
let x = 10;
console.log(x);    // Output : 10

{
let x = 2;
console.log(x);   // Output : 2
}

console.log(x);   // Output :10        
    

let can be updated but not re-declared.

        
let message = "Hello World";

if (true) {
let message = "How Are you";
console.log(message);      // Output :  "How Are you"
}

console.log(message);      // Output : "Hello World"        
    

This gives no error because this fact makes let a better choice than var. When using let, you don't have to bother if you have used a name for a variable before as a variable exists only within its scope.

        
let a = 10

// It is allowed
a = 20

console.log(a);                 // Output : 20        
    

From above example , we can assign different value to variable.

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Ankit Patel

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