The difference between let and const in js

let and const are different ways of declaring variables in JavaScript. The main difference lies in scope and assignment rules. Scope: let is block level, const is global or block level; assignment rules: let can be reassigned, const cannot be reassigned.

##The difference between let and const in JavaScript

let and const are two ways of declaring variables in JavaScript. The main difference between them is scope and assignment rules.

Scope

• #let Declared variables have block scope, which means they are only within the block in which they are declared. efficient.
• const Declared variables have either global or block-level scope, depending on where they are declared.

Assignment rules

• let Allows reassignment of variables.
• const Reassignment of variables is not allowed. Once declared, its value cannot be changed.

Detailed comparison

FeaturesScopeBlock LevelGlobal/Block LevelAssignmentCan be reassignedCannot be reassignedPurposeUsed when needed Variables that change within a blockUsed to declare unchanged values ​​or objectsDeclaration method##const = ; ##Duplicate declarationCan be declared repeatedly in the same blockCannot be declared repeatedly in the same block or scope##Example

	let	const
	let

// let 声明的变量可重新赋值
let count = 10;
count++; // count 变成 11

// const 声明的变量不可重新赋值
const PI = 3.14;
PI++; // 报错：Assignment to constant variable

Summary

let and

const

are important keywords for declaring variables in JavaScript. They provide different scope and assignment rules. . let is used for variables that need to be changed, while const is used to declare immutable values ​​or objects.

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