Introduction to Set object in JavaScript (with examples)

This article brings you an introduction to the Set object in JavaScript (with examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Create a Set object instance

Set object allows you to store a unique value of any type, whether it is a primitive value or an object reference

1.Constructor

Syntax: new Set([iterable])
Parameters:
iterable If an iterable object is passed, all its elements will be added to the new Set; If this parameter is not specified or its value is null, the new Set will be empty

    let arr = [1,2,2,3];
    let mySet = new Set(arr);
    console.log(mySet); // Set(3) {1, 2, 3}

2. Set instance attribute

1.size attribute will return the Set object The number of elements in

    let mySet = new Set();
    mySet.add(1);
    mySet.add(5);
    mySet.add("some text");
    console.log(mySet.size); // 3

3. Set instance method

1.add() method is used to add a specified value to the end of a Set object

Syntax: mySet.add(value)

Parameters: value required, the value of the element that needs to be added to the Set object

    let mySet = new Set();
    mySet.add(1);
    mySet.add(5).add("some text"); // 可以链式调用

    console.log(mySet); // Set [1, 5, "some text"]

2.delete() method can be used from a Set object Delete the specified element in

Syntax: mySet.delete(value)

Parameters: value The element to be deleted

Return value: Returns true if deleted successfully, otherwise returns false

    let mySet = new Set();
    mySet.add("foo");
    mySet.delete("foo"); // 返回 true，删除成功
    console.log(mySet.size); // 0

3.clear() method is used to clear all elements in a Set object

Syntax: mySet.clear()

    let mySet = new Set();
    mySet.add(1);
    mySet.add("foo");
    console.log(mySet.size);       // 2

    mySet.clear();
    console.log(mySet.size);       // 0

4.has() method returns a Boolean value to indicate whether the corresponding value value exists in the Set object

Syntax: mySet.has(value)

Parameters:

Value is required, whether it exists in the Set object

Return value: If the specified value (value) exists in the Set object, return true; otherwise, return false

    let mySet = new Set();
    mySet.add("foo");

    console.log(mySet.has("foo"));  // true
    console.log(mySet.has("bar"));  // false

5.entries()

Syntax: mySet. entries()

Return value: a new array iterator object containing the form [value, value], value is each element in the given collection, and the order of the iterator object elements is the elements in the collection object Insertion order

    let mySet = new Set();
    mySet.add("foobar");
    mySet.add(1);
    mySet.add("baz");

    let setIter = mySet.entries();

    console.log(setIter.next().value); // ["foobar", "foobar"]
    console.log(setIter.next().value); // [1, 1]
    console.log(setIter.next().value); // ["baz", "baz"]

6.values()

Syntax: mySet.values() or mySet.keys()

Return value: Return an Iterator object, this object Contains each element in the original Set object in the order in which the Set object was inserted

    let mySet = new Set();
    mySet.add("foo");
    mySet.add("bar");
    mySet.add("baz");

    let setIter = mySet.values();
    console.log(setIter.next().value); // "foo"
    console.log(setIter.next().value); // "bar"
    console.log(setIter.next().value); // "baz"

7.forEach()

Syntax: mySet.forEach(callback[, thisArg])

Parameters:
callback function that will be executed for each element
thisArg When executing the callback function, it can be used as this

    let mySet = new Set(["foo","bar",undefined]);
    mySet.forEach((value1,value2,set) => {
        console.log("key =",value1,",value =",value2); // key = foo ,value = foo
    });

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