In the browser
> this === window // => true
> "use strict";
this === window // => true
In node
a. 命令行
> node // => 进入node
> this === global // => true
b. node执行以下文件node index.js
// index.js
console.log(this === global) // => false
console.log(this === module.exports) // => true
c. in function call
function func () {
console.log(this === global) // => true
}
func()
"use strict";
function func () {
console.log(this === undefined) // => true
}
func()
function func () {
"use strict";
console.log(this === undefined) // => true
}
func()
e. in constructor call
function Person (firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
const person = Person("Jane", "Doe")
console.log(person) // => undefined
function Person (firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
const person = Person("Jane", "Doe")
console.log(person) // => undefined
console.log(global.firstName) // => Jane
console.log(global.lastName) // => Doe
// output:
// this.firstName = firstName;
// ^
//
// TypeError: Cannot set property 'firstName' of undefined ...
"use strict";
function Person (firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
const person = Person("Jane", "Doe")
console.log(person)
console.log(global.firstName)
console.log(global.lastName)
"use strict";
function Person (firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
const person = new Person("Jane", "Doe")
console.log(person) // => Person { firstName: 'Jane', lastName: 'Doe' }
console.log(global.firstName) // => undefined
console.log(global.lastName) // => undefined
