1. 值傳遞與引用傳遞

1.1 值傳遞

• 值傳遞發(fā)生在基本數(shù)據(jù)類型中

        let a = 10;
        let b = a;
        console.log(a, b); //10 10
        a = 5;
        console.log(a, b); //5 10

1.2 引用傳遞

• 發(fā)生在引用類型，數(shù)組，對象

        let s1 = {
            x: 1,
            y: 1
        };
        console.log(s1);
        // {x:1, y:1}
        let s2 = s1;
        console.log(s2);
        // {x:1, y:1}
        console.log(s1 === s2);
        // true
        s1.x = 10;
        console.log(s1);
        // {x:10, y:1}
        console.log(s2);
        // {x:10, y:1}

1.3 傳參

• 函數(shù)中，始終是值傳遞
• 傳入對象，更新對象的屬性仍屬于值傳遞，因?yàn)閷ο鬀]有被改變

        //基本類型
        const f1 = x => x = 10;
        let p = 5;
        f1(p);
        console.log(p);
        //對象
        const f2 = (obj) => { obj.age = 22; obj = {}; };
        let o = {
            age: 10,
            id: 0001
        }
        console.log(o);
        // {age:10, id:1}
        f2(o);
        console.log(o);
        // {age:22, id:1}

*

• 深拷貝：值傳遞
• 淺拷貝：引用傳遞

2. 模板字面量

• 字符串字面量+變量插值（嵌入到字符串）

        let name = "Tom";
        let greet = `Hello, ${name}`;
        console.log(greet);
        let stu = {
            id: 1112,
            name: "Em",
            age: 25,
            married: false
        }
        let stuInfo = `
        <div>
            <p>ID: ${stu.id}</p>
            <p>姓名：${stu.name}</p>
            <p>年齡：${stu.age}</p>
            <p>已婚：${stu.married}</p>
            </div>
        `;
        console.log(stuInfo);
        document.write(stuInfo);

2.1 標(biāo)簽函數(shù)

• 第一個(gè)參數(shù)：字符串本身元素組成的數(shù)組
• 第二個(gè)及以后：插值/插值組成的數(shù)組

        //少量參數(shù)
        let sum = (strs, a, b) => {
            console.log(strs);
            console.log(a, b);
        }
        let a = 5;
        let b = 10;
        let c = 20;
        sum`${a}+${b}=`;
        //多個(gè)參數(shù)
        sum = (strs, ...arr) => {
            console.log(strs);
            console.log(arr);
        }
        sum`${a}+${b}+${c}=`;

3. 解構(gòu)

3.1 數(shù)組解構(gòu)

        let arr = [1, 2, 3];
        let [a, b] = arr;
        console.log(a, b);
        // 1 2
        let c;
        [a, b, c] = arr;
        console.log(c);
        // 3
        arr = [1, 2, 3, 4, 5, 6, 7];
        [a, b, ...c] = arr;
        console.log(a, b, ...c);
        // 1 2 3 4 5 6 7
        [, , , , , c,] = arr;
        console.log(c);
        // 6
        // let [x, y] = [8, 9];
        x = 80;
        y = 90;
        console.log(x, y);
        // 80 90
        [y, x] = [x, y];
        console.log(x, y)
        // 90 80

3.2 對象解構(gòu)

        let stu = { name: "Tom", age: 22 };
        ({ name, age } = stu);
        // let { name, age } = stu;
        console.log(name, age)
        // Tom  22

3.3 參數(shù)解構(gòu)

        let sum = ([a, b]) => a + b;
        console.log(sum([60, 60]));
        // 120
        let stu1 = ({ name, age }) => [name, age];
        console.log(stu1({ name: "Em", age: 25 }));
        //["Em", 25]

3.4 對象簡化

• 如果對象的屬性與變量作用域相同且同名，可以寫作：

        x = 90, y = 80;
        let user = {
            x,
            y
        }
        console.log(user);
        // {x: 90, y: 80}

4 bind() call() apply() 函數(shù)

• 默認(rèn)的this關(guān)鍵字指向window
• 在對象中作為屬性的函數(shù)里，this指向的是當(dāng)前的對象
• 這三個(gè)函數(shù)用來改變this關(guān)鍵字的指向

        let stu = {
            name: "Em",
            age: 30
        }
        let name = "hehe";
        let obj = {
            name: "Tom",
            age: 22,
            foo: function () {
                console.log("Name: " + this.name);
                console.log("Age: " + this.age);
            }
        }
        console.log(this.name);
        obj.foo();
        obj.foo.bind(stu)();
        obj.foo.call(stu);
        obj.foo.apply(stu);

• 若函數(shù)有參數(shù)需傳入：

        obj = {
            name: "Tom",
            age: 22,
            foo: function (i, s) {
                console.log("Name: " + this.name);
                console.log("Age: " + this.age);
                console.log("Interest: " + i);
                console.log("Sport: " + s);
            }
        }
        obj.foo.bind(stu, "Xbox", "Tennis")();
        obj.foo.apply(stu, ["PS4", "Badminton"]);
        obj.foo.call(stu, "Switch", "Basketball");

5. 訪問器屬性 Getter Setter

• 方法以屬性的方式使用
• 簡化語法

        let item = {
            name: "unknown",
            price: 0,
            amount: 0,
            set setName(name) {
                this.name = name;
            },
            set setPrice(price) {
                this.price = price;
            },
            get addItem() {
                this.amount++;
            },
            get getName() {
                return this.name;
            },
            get getPrice() {
                return this.price;
            },
            get getAmount() {
                return this.amount;
            }
        }
        item.addItem;
        console.log(item.getAmount);
        item.setName = "iPad";
        console.log(item.getName);
        item.setPrice = "199";
        console.log(item.getPrice);
        //1
        //iPad
        //199

6. 流程控制

6.1 if 語句

• 語法

      if(true) return a = 1;
         else return a = 2;

• 當(dāng)只有執(zhí)行語句只有一行時(shí)，{}括號可以省略，多行時(shí)不可以

        let a = 1;
        if (a > 60)
            console.log(true);
        else
            console.log(false);
            // false

• 多個(gè)分支時(shí)

        let foo = (speed) => {
            if (speed < 60 && speed >= 0) {
                console.log("too slow");
            } else if (speed >= 60 && speed <= 100) {
                console.log("just right");
            } else if (speed > 100 && speed < 200) {
                console.log("too fast");
            } else {
                console.log("???");
            }
        }
        let currentSpeed = 80;
        foo(currentSpeed);
        currentSpeed = 30;
        foo(currentSpeed);
        currentSpeed = 150;
        foo(currentSpeed);
        currentSpeed = -1;
        foo(currentSpeed);

6.2 switch 語句

• 語法

    switch(true) {
        case a:
        ...;
        break;
        case b:
        ...;
        break;
        default:
        ...;
        break;
    }

*case 也可以是表達(dá)式表示多個(gè)值，如：

case a>0&&a<10:
console.log(true);

但多用于單個(gè)值的判斷

        let animal = "cat";
        switch (animal) {
            case "cat":
                console.log("貓");
                break;
            case "dog":
                console.log("狗");
                break;
            default:
                break;
        }
        //貓

6.3 三元運(yùn)算符

• 用于簡化雙分支

        currentSpeed = 2000;
        animal = "cat";
        console.log(currentSpeed <= 200 ? "OK" : "Boom");
        //Boom
        console.log(animal === "cat" ? true : false);
        //true

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