物件內可以放function

學生考了幾分

var exam = {}
console.log(exam)

exam = {
    title: "數學測驗",
    score: 95,
    student: "Tea",
    nickname: ["茶", "抹茶"],
    notify: function () {
        alert(exam.student + "考了" + exam.score + "分!")
    }
}
console.log(exam.notify) // 沒加小括號()，只會印出 function 物件
/*
ƒ () {
        alert(exam.student + "考了" + exam.score + "分!")
    }
    */

exam.notify()

計算考試分數

var score = {
    math: 95,
    english: 80,
    chinese: 77,
    avg: function () {
        var total = score.math + score.english + score.chinese
        return total / 3
    }
}

console.log(score.avg())

多個物件組成的陣列

var scores = [
    {student: "Jason", score: 95},
    {student: "Tom", score: 90},
    {student: "Kate", score: 88},
]

console.log(scores[2].student + "考了" + scores[2].score + "分");

迴圈

for

for(var i = 0; i < 10; i++){
    console.log(i);
}

for in list

var scores = [
    {student: "Jason", score: 95},
    {student: "Tom", score: 90},
    {student: "Kate", score: 88},
]


for(i = 0; i < scores.length; i++){
    console.log("學生:", scores[i].student + "考了" , scores[i].score,"分")
}

映射 Map

存放Key、Value
宣告時要用new

正確用法

var m = new Map();
m.set("name","Tea");    // 新增資料到Key中
console.log(m)
m.set("name","Pencil"); // 同樣的Key後面覆蓋前面
console.log(m)

console.log(m.has('name')); // true
console.log(m.get('name')); // Pencil

以下為在其他語言中看似正確，在JS裡卻是 錯誤的Map用法
(雖然可以用，但與上面的get、has就像兩個世界一樣毫無相干)

剛從其他語言轉過來時，覺得錯誤用法超級合理的。

var m = new Map();
m['name'] = "Tea";
m['name'] = "Pencil";

console.log(m['name']);

不過稍微看了一下，這錯誤的map用法是屬於Object物件的屬性原生用法，
也許設計當初是怕與這搞混淆才區別開來吧。

var m =  Object();
m['name'] = "123"
console.log(m['name']);

錯誤用法的Key、Value會跑到屬性欄位去
也許這段程式碼(在Chrome console上的輸出)，能較容易理解兩者區別：

var m = new Map();
m['name1'] = "Tea";
m['name2'] = "Pencil";

console.log("錯誤用法:")
console.log(m);



m.set("name1","Tea");
m.set("name2","Pencil");

console.log("加上了正確用法:")
console.log(m)

七種迭代map的寫法

var m = new Map();
m.set("name1","Tea");
console.log(m)
m.set("name2","Pencil");
console.log(m)

console.log(m.size); // 2
console.log(m.keys()); // {"name1", "name2"}

for (var key of m.keys()){
    console.log(key);
}

for (var value of m.values()){
    console.log(value);
}

for (var [key, value] of m){
    console.log(key, value);
}

for (var [key, value] of m.entries()){
    console.log(key, value);
}

// 以上四種for迴圈，以下三種forEach

m.forEach(function (value){
    console.log(value);
})

m.forEach(function (value, key){
    console.log(value, key);
})

m.forEach(function (value, key, map){
    console.log(value, key, map);
})