【後转前要多久】# Day24 JS - JavaScript 物件、函式

物件内可以放function

学生考了几分

var exam = {}
console.log(exam)

exam = {
    title: "数学测验",
    score: 95,
    student: "Tea",
    nickname: ["茶", "抹茶"],
    notify: function () {
        alert(exam.student + "考了" + exam.score + "分!")
    }
}
console.log(exam.notify) // 没加小括号()，只会印出 function 物件
/*
ƒ () {
        alert(exam.student + "考了" + exam.score + "分!")
    }
    */

exam.notify()

计算考试分数

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())

多个物件组成的阵列

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");

回圈

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("学生:", scores[i].student + "考了" , scores[i].score,"分")
}

映射 Map

存放Key、Value
宣告时要用new

正确用法

var m = new Map();
m.set("name","Tea");    // 新增资料到Key中
console.log(m)
m.set("name","Pencil"); // 同样的Key後面覆盖前面
console.log(m)

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

以下为在其他语言中看似正确，在JS里却是 错误的Map用法
(虽然可以用，但与上面的get、has就像两个世界一样毫无相干)

刚从其他语言转过来时，觉得错误用法超级合理的。

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

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

不过稍微看了一下，这错误的map用法是属於Object物件的属性原生用法，
也许设计当初是怕与这搞混淆才区别开来吧。

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

错误用法的Key、Value会跑到属性栏位去
也许这段程序码(在Chrome console上的输出)，能较容易理解两者区别：

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

console.log("错误用法:")
console.log(m);



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

console.log("加上了正确用法:")
console.log(m)

七种迭代map的写法

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);
}

// 以上四种for回圈，以下三种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);
})