What are the es6 set methods?

es6 set methods can be divided into two categories: 1. Operation methods "add(value)", "delete(value)", "has(value)", clear(); 2. Traversal method keys (), values(), entries(), forEach().

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

ES6 provides a new data structure Set. It is similar to an array, but the values ​​of the members are unique and there are no duplicate values.

Many times we call Set a set. However, a Set can be a set, but a set is not necessarily a Set.

Features: Uniqueness=>No duplication=>Ability to deduplicate data.

Creating a Set

Set itself is a constructor, and the constructor is called to generate the Set data structure.

关键词　标识符　= new Set();

Example

let i = new Set();

Set function can accept an array (or array-like object) as a parameter for data initialization.

let i = new Set([1, 2, 3, 4, 4]);  //会得到　　set{1, 2, 3, 4,}

Note: If there are duplicate values ​​given during initialization, they will be automatically removed. Collections do not have a literal declaration method and can only be declared using the new keyword.

Attributes of Set

There is only one commonly used attribute: size--returns the total number of members of the Set instance.

let s = new Set([1, 2, 3]);
console.log( s.size ); // 3

Set methods

The methods of Set instances are divided into two categories: operation methods (for data operations) and traversal methods (for traversal data).

Operation method:

• add(value)　　Add data and return a new Set structure

• delete(value)　Delete data and return a Boolean value, indicating whether the deletion was successful

• has(value)　Check whether a certain data exists and return a Boolean value

• clear()　　　Clear all data, no return value

let set = new Set([1, 2, 3, 4, 4]);
// 添加数据 5
let addSet = set.add(5);
console.log(addSet); // Set(5) {1, 2, 3, 4, 5}

// 删除数据 4s
let delSet = set.delete(4);
console.log(delSet); // true 此处返回值是个boolean 表示 是否删除成功

// 查看是否存在数据 4
let hasSet = set.has(4);
console.log(hasSet); // false

// 清除所有数据
set.clear();
console.log(set); // Set(0) {}

Traversal method:

Set provides three The traverser generates functions and a traversal method.

• keys()　　 Returns a traverser of key names

• values()　　 Returns a traverser of key values

• entries()　 Return a traverser of key-value pairs

• forEach()　 Use the callback function to traverse each member

let color = new Set(["red", "green", "blue"]);
for(let item of color.keys()){
 console.log(item);
}
// red
// green
// blue
for(let item of color.values()){
 console.log(item);
}
// red
// green
// blue
for(let item of color.entries()){
 console.log(item);
}
// ["red", "red"]
// ["green", "green"]
// ["blue", "blue"]
color.forEach((item) => {
 console.log(item)
})
// red
// green
// blue

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