Detailed explanation of examples of set-map data structure in ES6-JS Tutorial-php.cn

Detailed explanation of examples of set-map data structure in ES6

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Release： 2017-06-26 09:12:31

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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);
}

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　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);
}

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　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);
}

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　 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);
}

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　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);})
}

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　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);
}

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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));
}

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　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);
}

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　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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