Details of the method of Set collection in JavaScript

Set Collection Overview

• Set collections are very similar to Arry arrays, but Set collections store keys, that is, there cannot be two keys with equal values ​​and data types in the Set collection.
• Set collections cannot be valued with subscripts
• Set collection has no length attribute but size
• Set collections can be converted into real arrays

How to create and use Set

Create a Set and add an existing variable:

// Create variablesconst a = "a";
const b = "b";
const c = "c";

// Create Setconst letters = new Set();

(a);
(b);
(c);

Add()

Adding elements to the collection will deduplicate, and adding repeated elements will only display one

var set = new Set()
(1)
(set); // {1}

var set = new Set().add(1).add([2,3,4])
(set); // {1, [2,3,4]}

var set = new Set([1,2,3,4,5,6]);
((123)); // {1, 2, 3, 4, 5, 6, 123} Instructions added successfully((1)); // {1, 2, 3, 4, 5,6,123} It means that duplicates were not added successfully

Clear()

Clear Set object

var set = new Set([1,2,3,4,5,6]);
()
(set); // {size: 0} Cleared successfully

Delete()

Delete values ​​in Set object

var set = new Set([1,2,3,4,5,6]);
((1));  // true means the deletion is successful((1));  // false indicates that the deletion failed because the collection no longer exists.(set);   // [2,3,4,5,6] 1Deleted

Entries()

The Entries() method returns an iterative object of an array that contains the key/value pairs of the array (key/value). The index value of the array in the iterative object is used as the key and the array element is used as the value.

var set = new Set([1,2,3,4,5]);
(set); // {1, 2, 3, 4, 5}
(()); // {1 => 1, 2 => 2, 3 => 3, 4 => 4, 5 => 5}

Has()

Determine whether a value in the Set object exists, returns true, does not exist, returns false

var set = new Set([1,2,3,4,5]);
((1)); // ture indicates that there is 1 in the Set object((6)); // false illustrateSetDoes not exist in the object6

ForEach()

Calling a callback for each element It has three parameters:

• .value：Optional, the value of the element in the Set object.
• .key：Optional Since the Set object has no key, the value of the key and the value of the value are the same.
• .setObj:Optional, Set object itself.

var set = new Set([1,2,3,4,5]);
((value,key,setObj)=>{
  (value,key,setObj);
})
// 1 1 {1, 2, 3, 4, 5}
// 2 2 {1, 2, 3, 4, 5}
....

Keys() and values()

Returns the key value array of Set object, and returns the value array of Set object

var set = new Set([1,2,3,4,5]);
(()); // {1, 2, 3, 4, 5}
(()); // {1, 2, 3, 4, 5}

Size

Returns the count of elements in the Set object

var set = new Set([1,2,3,4,5]);
();  // 5

Set of methods and properties of Set objects

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