<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Document</title> </head> <body> </body> <script> // set:数组和对象的映射,或抽象 var s = new Set(["hello",7,"world",7,"world",7,"world"]); console.log(s);//{"hello", 7, "world"} set不会重复 console.log(typeof s);//object console.log(s[0]);//u console.log(s[1]);//u console.log(s[2]);//u console.log(s.length);//u for(var i of s){ console.log(i)//hello 7 world } var s = new Set(); s.add(3) s.add(4) s.add(5) s.add("3") console.log(s)//Set(4) {3, 4, 5, "3"}// Set集合是默认去重复的,但前提是两个添加的元素严格相等 所以3和"3"不相等,两个new出来的字符串不相等 for(var i of s.keys()){ //数组keys就是他本身 console.log(i) //3 4 5 3 } for(var i of s.values()){ console.log(i) //3 4 5 3 } for(var i of s.entries()){ console.log(i)//[3,3] [4,4] [5,5] [3,3] } // map 关于遍历的方法 由于Set集合本质上还是一个map,因此会有以下几种奇怪的遍历方法 var m = new Map(); m.set("name","admin"); m.set("age",18); console.log(m);//Map(2) {"name" => "admin", "age" => 18} //不是箭头函数 console.log(typeof m);//object console.log(m.get("name"));//admin console.log(m.get("age"));//18 console.log(m.name); //undefined console.log(m.age);//u for(var i of m){ console.log(i) // ["name", "admin"] ["age", 18] } for(var i of m.keys()){ console.log(i) //name age } for(var i of m.values()){ console.log(i) //admin 18 } for(var i of m.entries()){ console.log(i) //["name", "admin"] ["age", 18] } </script> </html>