[ES6] 18. Map

ES6 provides Map, it is a set of k-v pair. Key can be number, string, object, function and even undefined.

var m = new Map();

Methods:

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1. set(k,v)

m.set("edition", 6)        // 键是字符串
m.set(262, "standard")     // 键是数值
m.set(undefined, "nah")    // 键是undefined

var hello = function() {console.log("hello");}
m.set(hello, "Hello ES6!") // 键是函数

2. get(k)

m.get(hello)  // Hello ES6!
m.get("edition")  // 6

3. has(k)

m.has("edition")     // true
m.has("years")       // false
m.has(262)           // true
m.has(undefined)     // true
m.has(hello)         // true

4. delete(k)

m.delete(undefined)
m.has(undefined)       // false

5. clear()

6. size()

m.size(); // 3
m.clear(); 
m.size(); // 0