JavaScript高级程序设计第四版学习记录-第四章变量、作用域与内存

发布日期：2021-05-14 11:06:32 浏览次数：22 分类：精选文章

本文共 1971 字，大约阅读时间需要 6 分钟。

JavaScript ?????????

JavaScript ???????????????????????????????? JavaScript ????????

1. ???????

? JavaScript ?????????? 6 ???????????

undefined

null

boolean?????

number????

string?????

symbol

???

????????? ???by value??????????????

???????????????????????????????????????????

?????????????????????????????????? ????by reference? ????????????????????????

2. ?????????

?? JavaScript ????????? ???????????????????????????????? ?????????????????????????????

2.1 ?????

?????? JavaScript ??????????

?????????????? window ???

?????????????? window ????

2.2 ?????

???????????????????????????????

??????????? arguments ????????????

2.3 ????

????????? ????????????????????

????????????????????????????????????????

3. ?????????

3.1 ??????

??????????????????????

???

let person = new Object();
person.name = "Nicholas";
console.log(person.name); // "Nicholas"

3.2 ??????

???????????????????????????? undefined?

???

let name = "Nicholas";
name.age = 27;
console.log(name.age); // undefined

4. ????????

4.1 ?????

???????????????????

???

let num1 = 5;
let num2 = num1; // num2 ??? 5

4.2 ?????

???????????????????????

???

let obj1 = new Object();
let obj2 = obj1; // obj1 ? obj2 ???????
obj1.name = "Nicholas";
console.log(obj2.name); // "Nicholas"

4.3 ??????

JavaScript ????????????

???

function setName(obj) {
  obj.name = "Nicholas";
}
let person = new Object();
setName(person);
console.log(person.name); // "Nicholas"

5. ??????

5.1 typeof ???

typeof ??????????

????
- undefined????????????????
- object???? null?
- ????string?number?boolean?symbol ? function?

5.2 instanceof ???

???????????????????

???

console.log(person instanceof Object); // true

6. ?????????

6.1 JavaScript ?????

JavaScript ?? ???? ?????????

????????

?????????

????????????????

6.2 ??????

????????????

?????
- ???????
- ?? delete ????????? null?

6.3 ????

????????????????????????????

???????????????????????

7. ??

???????????????????? typeof ? instanceof ????

???????????????????????????

?????????????????????????????????

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