ES6基础语法之Map和Set对象
作者:農碼一生
这篇文章介绍了ES6基础语法之Map和Set对象,文中通过示例代码介绍的非常详细。对大家的学习或工作具有一定的参考借鉴价值,需要的朋友可以参考下
一、Map对象
Map 对象保存键值对。任何值(对象或者原始值) 都可以作为一个键或一个值。
Map中的键值是有序的。
let myMap = new Map(); myMap.set("23","乔丹"); myMap.set("33","皮蓬"); let name = myMap.get("33"); console.log(name); //皮蓬 let has = myMap.has("24"); //查找是否含有此键 console.log(has); //false
Map的迭代:
let myMap = new Map(); myMap.set("23","乔丹"); myMap.set("33","皮蓬"); myMap.set("99","罗德曼"); //循环键 for (let key of myMap.keys()) { console.log(key); } //循环值 for (let value of myMap.values()) { console.log(value); } //循环键和值 for (let [key, value] of myMap) { console.log(key + " = " + value); } //或 for (let [key, value] of myMap.entries()) { console.log(key + " = " + value); } //使用forEach循环 myMap.forEach(function(value,key){ console.log(key + "=" + value); },myMap);
Map 与 Array的转换:
//二维数组转换成map对象 let arr = [[23,"乔丹"],[33,"皮蓬"],[99,"罗德曼"]]; let myMap = new Map(arr); for (let [key, value] of myMap) { console.log(key + " = " + value); } //map对象转换成二维数组 let outArr = Array.from(myMap); console.log(outArr);
Map的克隆:
let myMap1 = new Map([[23,"乔丹"],[33,"皮蓬"],[99,"罗德曼"]]); let myMap2 = new Map(myMap1); for (let [key, value] of myMap2) { console.log(key + " = " + value); }
Map的合并(合并两个 Map 对象时,如果有重复的键值,则后面的会覆盖前面的)
let myMap1 = new Map([[23,"乔丹"],[33,"皮蓬"],[99,"罗德曼"]]); let myMap2 = new Map([[23,"詹姆斯"],[24,"科比"],[11,"姚明"]]); let myMap = new Map([...myMap1,...myMap2]); //合并之后詹姆斯会替换乔丹 for (let [key, value] of myMap) { console.log(key + " = " + value); }
二、Set对象
Set 对象允许你存储任何类型的唯一值,无论是原始值或者是对象引用。
Set 对象存储的值总是唯一的,所以需要判断两个值是否恒等。有几个特殊值需要特殊对待:
(1) +0 与 -0 在存储判断唯一性的时候是恒等的,所以不重复;
(2) undefined 与 undefined 是恒等的,所以不重复;
(3) NaN 与 NaN 是不恒等的,但是在 Set 中只能存一个,不重复。
let mySet = new Set(); mySet.add(1); mySet.add("hello"); //这里体现了类型的多样性 mySet.add(2); mySet.add(1); //这里添加不了,这里体现了值的唯一性 console.log(mySet); //{1,"hello",2} console.log(mySet.has(3)); //false, 是否含有3
以下代码体现了对象之间引用不同不恒等,即使值相同,Set 也能存储
let mySet = new Set(); let o = {a: 1, b: 2}; mySet.add(o); mySet.add({a: 1, b: 2}); console.log(mySet);
Set类型转换:
//Array 转 Set let arr = ["乔丹","皮蓬","罗德曼"]; let mySet = new Set(arr); console.log(mySet); //Set转Array(使用...) let mySet = new Set(); mySet.add("乔丹"); mySet.add("皮蓬"); mySet.add("罗德曼"); let arr = [...mySet]; console.log(arr); //字符串转Set(注:Set中toString方法是不能将Set转换成String) let mySet = new Set("hello"); console.log(mySet); //h e l o (两个l只出现一次)
Set对象的作用:
//数组去重复 let mySet = new Set([1,2,1,2,3,3,4,5,6,4,7]); let arr = [...mySet]; console.log(arr); //1,2,3,4,5,6,7 //数组求并集 let a = new Set([1, 2, 3]); let b = new Set([4, 3, 2]); let union = new Set([...a, ...b]); let arr = [...union]; console.log(arr); //1, 2, 3, 4 //数组求交集 let a = new Set([1, 2, 3]); let b = new Set([4, 3, 2]); let intersect = new Set([...a].filter(p=>b.has(p))); let arr = [...intersect]; console.log(arr); //2, 3
到此这篇关于ES6基础语法之Map和Set对象的文章就介绍到这了。希望对大家的学习有所帮助,也希望大家多多支持脚本之家。