Deconstruction assignment in ES6

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Deconstruction assignment in ES6

According to the deconstruction of the original value, a part of the original value is quickly obtained (quickly assigned to a variable)

Deconstruction and assignment of arrays

Deconstruction assignment itself is the syntax specification of ES6. It doesn't matter what keywords are used to declare these variables

let ary = [12,23,34];

//Traditional value assignment
// let a = ary[0],
//     b = ary[0],
//     c = ary[0];
//
// console.log(a, b, c);
//1
let [a,b,c] = [12,23,34];
console.log(a, b, c);//12,23,34
//2
var [a,b,c] = [12,23,34];
console.log(a, b, c);//12,23,34
//3
[a,b,c] =[12,23,34];
console.log(a, b, c);//12,23,34
//This is equivalent to adding global attributes to window, but in strict mode, declaration variable "use strict" such as var/let cannot be used
//4
~function () {
    [a,b,c] =[12,23,34];
    //This is equivalent to adding global attributes to window, but declaration variables such as var/let cannot be used in strict mode
    console.log(a, b, c);//12,23,34
}();

//5
~function () {
    [a,b,c] =[12,23,34];
    //This is equivalent to adding global attributes to window, but declaration variables such as var/let cannot be used in strict mode
}();
console.log(a, b, c);//12,23,34
//6
~function () {
    let [a,b,c] =[12,23,34];
    //Private attributes
}();
console.log(a, b, c);//Report errors

The deconstruction and assignment of multi-dimensional array can enable us to get the required results quickly

//let ary = [12,[23,34],[45,56,[67,78]]];
//let A = ary[1][1];
let [,[,A],[,B,[,C]]] = [12,[23,34],[45,56,[67,78]]];
console.log(A, B, C);//34 56 78

If you only want to get some items in the front of the array, the later structure does not need to be completed

let [D] = [12,23,34];
console.log(D); 
let [,E] = [12,23,34];
console.log(E); //=>23

In the deconstruction assignment, we can set a default value for an item

let [,,,E] = [12,23,34];
console.log(E); //=>undefined

let [,,,F = 0] = [12,23,34];
console.log(F); //=>0

In the deconstruction assignment, the extension operator of... xxx is supported

let [A,...B] = [12,23,34,45,56];
console.log(A, B);//->12 [ 23, 34, 45, 56 ]

let [...C] =[12,23,34,45,56];
console.log(C);//[12, 23, 34, 45, 56] array clone
let [E,...D,F] = [12,23,34,45,56];
console.log(E, D, F);//Rest element must be last element the extension operator can only appear at the end of a deconstruction assignment
let[G,,,...H] = [12,23,34,45,56];
console.log(G, H); //12 [ 45, 56 ]

Posted by BenInBlack on Thu, 02 Apr 2020 07:55:56 -0700

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