Is the set type in es6 ordered?

The set type in es6 is ordered. The set type is a new ordered list collection in es6, which contains some independent non-repeating values; the traversal order of set is the insertion order. When a function list saved by set is called, it is called in the specified order, so The set type is ordered.

The operating environment of this article: Windows 10 system, Vue version 2.9.6, DELL G3 computer.

Is the set type in es6 ordered?

Yes, you can find the answer in the official Set. The traversal order of Set is the insertion order.

This feature is sometimes very useful. For example, using Set to save a list of callback functions can ensure that they are called in the order they are added when called.

Basic concepts

The new Set type in ES6 is an ordered list that contains some independent non-repeating values.

* Whether members are duplicated or not is determined internally by the Object.is() method in the Set collection.

Set is a new ordered list collection added in ES6, which does not contain duplicate items. Previously, we usually used objects (Object) or arrays (Array) to implement collections without duplicate items. However, the object will perform toString() operation on the key, which will cause some keys to accidentally overwrite the previous data; if the key itself is an object, toString() will not get the desired result, as follows:

JSvar o = {};
var key1 = 2;
var key2 = { toString : function() { return 2 } };
var key3 = { x : 1 };
var key4 = { y : 2 };
o[key1] = 1;
o[key2] = 2;
o[key3] = 3;
o[key4] = 4;
// o : Object {2: 2, [object Object]: 4}

Arrays can store any type of data, but data deduplication needs to be implemented by yourself.

Set supports the add(item) method, which is used to add any type of element to the Set. If it has already been added, it will be automatically ignored; the has(item) method is used to detect whether the specified element exists in the Set; delete(item ) method is used to delete specified elements from Set; clear() is used to clear Set; use the size attribute to obtain the length of Set. As follows:

JSvar set = new Set();
set.add(window);
set.has(window); // trueset.size; // 1set.add(window);
set.add(1);
set.size; // 2set.delete(window);
set.has(window); // falseset.clear();
set.size; // 0

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