2.2 ES6 Destructuring Assignment
Category ES6 Tutorial
Overview
Destructuring assignment is an extension of the assignment operator.
It is a pattern matching for arrays or objects, and then assigns values to the variables within.
In terms of code writing, it is concise and readable, with clearer semantics; it also facilitates the retrieval of data fields in complex objects.
Destructuring Models
In destructuring, the following two parts are involved:
- The target of destructuring, the left part of the destructuring assignment expression.
Array Model Destructuring (Array)
Basic
let [a, b, c] = [1, 2, 3];
// a = 1
// b = 2
// c = 3
Nested
let [a, [[b], c]] = [1, [[2], 3]];
// a = 1
// b = 2
// c = 3
Omissible
let [a, , b] = [1, 2, 3];
// a = 1
// b = 3
Partial Destructuring
let [a = 1, b] = []; // a = 1, b = undefined
Rest Operator
let [a, ...b] = [1, 2, 3];
//a = 1
//b = [2, 3]
Strings, etc.
In array destructuring, if the target of destructuring is an iterable object, destructuring assignment can be performed. Iterable objects are data that implement the Iterator interface.
let [a, b, c, d, e] = 'hello';
// a = 'h'
// b = 'e'
// c = 'l'
// d = 'l'
// e = 'o'
Destructuring Default Values
let [a = 2] = [undefined]; // a = 2
When the destructuring pattern has a match, and the match result is undefined, the default value is triggered as the return result.
let [a = 3, b = a] = []; // a = 3, b = 3
let [a = 3, b = a] = [1]; // a = 1, b = 1
let [a = 3, b = a] = [1, 2]; // a = 1, b = 2
a and b match result is undefined, triggering the default value:
a = 3; b = a =3
a is normally destructured and assigned, match result: a = 1, b match result is undefined, triggering the default value:
b = a =1
a and b are normally destructured and assigned, match results:
a = 1, b = 2
Object Model Destructuring (Object)
Basic
let { foo, bar } = { foo: 'aaa', bar: 'bbb' };
// foo = 'aaa'
// bar = 'bbb'
let { baz : foo } = { baz : 'ddd' };
// foo = 'ddd'
Nested and Omissible
let obj = {p: ['hello', {y: 'world'}] };
let {p: [x, { y }] } = obj;
// x = 'hello'
// y = 'world'
let obj = {p: ['hello', {y: 'world'}] };
let {p: [x, { }] } = obj;
// x = 'hello'
Partial Destructuring
let obj = {p: [{y: 'world'}] };
let {p: [{ y }, x ] } = obj;
// x = undefined
// y = 'world'
Rest Operator
let {a, b, ...rest} = {a: 10, b: 20, c: 30, d: 40};
// a = 10
// b = 20
// rest = {c: 30, d: 40}
Destructuring Default Values
let {a = 10, b = 5} = {a: 3};
// a = 3; b = 5;
let {a: aa = 10, b: bb = 5} = {a: 3};
// aa = 3; bb = 5;
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** Xiao Lan
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