What does es6 set mean?

set means "set" and is a new data structure provided by ES6. It is similar to an array, but the values ​​of the members are unique and there are no duplicate values. Set objects allow users to store unique values ​​of any type, whether primitive values ​​or object references.

The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.

What is Set?

Set (set) is a new data structure provided by ES6, which is similar to an array, but the values ​​of the members are unique and there are no duplicate values.

Set objects allow you to store unique values ​​of any type, whether primitive values ​​or object references.

Set itself is a constructor used to generate the Set data structure.

Special values ​​in Set:

The value stored in a Set object is always unique, so it is necessary to determine whether the two values ​​are equal. There are several special values ​​that require special treatment:

• 0 and -0 are identical when storing and judging uniqueness, so they are not repeated;

• undefined and undefined are identical, so they are not repeated;

• NaN and NaN are not identical, but only one can be stored in the Set, and they are not repeated.

Set usage scenarios

1. Used for array deduplication

let arr = [3, 5, 2, 2, 5, 5];
let setArr = new Set(arr)     // 返回set数据结构  Set(3) {3, 5, 2}

//方法一   es6的...解构
let unique1 =  [...setArr ];      //去重转数组后  [3,5,2]

//方法二  Array.from()解析类数组为数组
let unique2 = Array.from(setArr )   //去重转数组后  [3,5,2]

2. Used for string deduplication

let str = "352255";
let unique = [...new Set(str)].join("");     // 352

3. Implement intersection, union and difference set

let a = new Set([1, 2, 3]);
let b = new Set([4, 3, 2]);

// 并集
let union = new Set([...a, ...b]);
// Set {1, 2, 3, 4}

// 交集
let intersect = new Set([...a].filter(x => b.has(x)));
// set {2, 3}

// （a 相对于 b 的）差集
let difference = new Set([...a].filter(x => !b.has(x)));
// Set {1}

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