问在哪种情况下，我应该更喜欢ES6映射而不是JavaScript对象？

EN

let s = new Set()
s.add("hello").add("goodbye")

let m = new Map()
m.set("hello", 42)
m.set(s, 34)
m.get(s) === 34
m.size === 2
for (let [ key, val ] of m.entries())
    console.log(key + " = " + val) 

var s = {}; 
s["hello"] = true; s["goodbye"] = true;

var m = {};
m["hello"] = 42; 
// no equivalent in ES5 
// no equivalent in ES5
Object.keys(m).length === 2;
for (key in m) {
    if (m.hasOwnProperty(key)) {
        var val = m[key];
        console.log(key + " = " + val);
    }
}

var a = {};

// Put value in map
a['hasOwnProperty'] = 1;

for(x in a) {
    // TypeError: a.hasOwnProperty is not a function
    if(a.hasOwnProperty(x)) {
        console.log(x);
    }
}