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1. Set data structure (use new to create a set collection, add elements through the add method, and obtain the length of the set collection through size)
{
let list = new Set();
list.add(5);
list.add(7);
console.log('size',list.size);
}There is another way to initialize (by passing the array directly)
{
let arr = [1,2,3,4,5];
let list = new Set(arr);
console.log('size',list.size);
}The elements in set cannot be repeated (Array deduplication can be carried out through this feature of set. Note: data type conversion will not be performed during the conversion process)
{
let list = new Set();
list.add(1);
list.add(2);
list.add(1);//不会报错 只是不会生效
console.log('list',list);
let arr=[1,2,3,1,'2'];
let list2=new Set(arr);
console.log('unique',list2);
}Some methods of set (add, delete, clear, has)
{
let arr=['add','delete','clear','has'];
let list=new Set(arr);
console.log('has',list.has('add'));//是否包含
console.log('delete',list.delete('add'),list);//清空
list.clear();
console.log('list',list);
}Traversal of set (keys and values return the values in the set)
{
let arr=['add','delete','clear','has'];
let list=new Set(arr); for(let key of list.keys()){
console.log('keys',key);
} for(let value of list.values()){
console.log('value',value);
} for(let [key,value] of list.entries()){
console.log('entries',key,value);
}
list.forEach(function(item){console.log(item);})
}WeakSet (the elements inside can only be objects, and it will not detect whether the added object is referenced elsewhere, and traversal is not supported without size clear)
{
let weakList=new WeakSet();
let arg={};
weakList.add(arg); // weakList.add(2);
console.log('weakList',weakList);
}2. Map data structure (Map is set through key/value, so the set method is used for setting and the get method is used for obtaining)
{
let map = new Map();
let arr=['123'];
map.set(arr,456);
console.log('map',map,map.get(arr));
}Another way to define Map (at the same time the size delete clear method is the same)
{
let map = new Map([['a',123],['b',456]]);
console.log('map args',map);
console.log('size',map.size);
console.log('delete',map.delete('a'),map);
console.log('clear',map.clear(),map);
}weakMap data structure (the same characteristics as setMap)
{
let weakmap=new WeakMap();
let o={};
weakmap.set(o,123);
console.log(weakmap.get(o));
}
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