About the difference between let and const in JavaScript (notes)

Table of contents

1. Main differences:
2. let generally declares variables
3. const is generally used to declare variables, arrays, and objects

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Main differences:

let:	General declaration of variables
const:	Generally used to declare constants, arrays, and objects (the address value cannot be modified)

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let generally declares variables

1. Declare variables

Example: let a;

        let b,c;

2. Variables cannot be declared repeatedly

Example: let start = 'aa'

       let start ='bb'    X

3. Block-level scope

 example:{

        let c = 'Hello'

        }      

        console.log(c)   X  cannot be quoted

4. There is no variable promotion

Example: console.log(song)

        let song = 'La La La'   the result is underfined

5.  Does not affect scope effects

example:

        {

        let school = 'Agricultural University'

        function fu(){

        console.log(school)

        }}

const is generally used to declare variables, arrays, and objects

1. Be sure to assign an initial value

Example: const A = 'Hello'

2. Generally use capital letters for constants (writing standards)

Example: const B = 'uppercase'

3. The value of a constant cannot be modified.

Example: A = 'Haha'          X

4. Block-level scope

example:{

        const O = 'UZI'

 }

5. Modification of elements of arrays and objects does not count as modification of constants, and no error is reported (because you change the address value)

Example: const TEST = ['a','b']

        TEST.push('c')