集合类型

var items = new Set();
items.add(5);
items.add("5");

console.log(items.size());    // 2

var items = new Set();
items.add(5);
items.add("5");
items.add(5);     // oops, duplicate - this is ignored

console.log(items.size());    // 2

var items = new Set([1, 2, 3, 4, 5, 5, 5, 5]);
console.log(items.size());    // 5

var items = new Set();
items.add(5);
items.add("5");

console.log(items.has(5));    // true
console.log(items.has(6));    // false

var items = new Set();
items.add(5);
items.add("5");

console.log(items.has(5));    // true

items.delete(5)

console.log(items.has(5));    // false

var items = new Set([1, 2, 3, 4, 5]);

for (let num of items) {
    console.log(num);
}

// element gets converted to a string
var data = {},
    element = document.getElementById("my-div");

data[element] = metadata;

var map = new Map();
map.set("name", "Nicholas");
map.set(document.getElementById("my-div"), { flagged: false });

// later
var name = map.get("name"),
    meta = map.get(document.getElementById("my-div"));

var map = new Map([ ["name", "Nicholas"], ["title", "Author"]]);

for (let key of map.keys()) {
    console.log("Key: %s", key);
}

for (let value of map.values()) {
    console.log("Value: %s", value);
}

for (let item of map.items()) {           这个是默认的
    console.log("Key: %s, Value: %s", item[0], item[1]);
}

// same as using map.items()   
for (let item of map) {
    console.log("Key: %s, Value: %s", item[0], item[1]);
}

var reporter = {
    report: function(key, value) {
        console.log("Key: %s, Value: %s", key, value);
    }
};

map.forEach(function(value, key, map) {
    this.report(key, value);
}, reporter);

for (let key in object) {

    // make sure it‘s not from the prototype or a function!
    if (object.hasOwnProperty(key) && typeof object[key] !== "function") {
        console.log("Key: %s, Value: %s", key, object[key]);
    }

}