347 lines
5.3 KiB
Markdown
347 lines
5.3 KiB
Markdown
# this练习
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注：document.write的题目 需要写出在页面上打印的结果
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1. 下面代码的执行结果是什么 为什么
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```
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var person = {
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firstName: "John",
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lastName : "Doe",
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id : 5566,
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fullName : function() {
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return this.firstName + " " + this.lastName;
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}
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};
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// 显示对象的数据
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document.getElementById("demo").innerHTML = person.fullName();
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```
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2. 下面代码的执行结果是什么 为什么
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```
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var x = this;
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document.getElementById("demo").innerHTML = x;
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```
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3. 下面代码的执行结果是什么 为什么
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```
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"use strict";
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var x = this;
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document.getElementById("demo").innerHTML = x;
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```
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4. 下面代码的执行结果是什么 为什么
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```
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document.getElementById("demo").innerHTML = myFunction();
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function myFunction() {
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return this;
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}
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```
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5. 下面代码的执行结果是什么 为什么
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```
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"use strict";
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document.getElementById("demo").innerHTML = myFunction();
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function myFunction() {
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return this;
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}
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```
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6. 下面代码的执行结果是什么 为什么
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```
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<body>
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<h2>JavaScript <b>this</b> 关键字</h2>
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<button onclick="this.style.display='none'">点我后我就消失了</button>
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</body>
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```
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7. 下面代码执行结果是什么 为什么
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```
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var person = {
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firstName : "John",
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lastName : "Doe",
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id : 5566,
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myFunction : function() {
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return this;
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}
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};
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// 显示表单数据
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document.getElementById("demo").innerHTML = person.myFunction();
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```
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8. 把第7题的对象中的属性和方法挨个打印在页面上
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9. 下面代码的执行结果是什么 为什么
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```
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var person = {
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firstName: "John",
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lastName : "Doe",
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id : 5566,
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fullName : function() {
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return this.firstName + " " + this.lastName;
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}
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};
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// 显示对象的数据
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document.getElementById("demo").innerHTML = person.fullName();
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```
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10. 下面代码的执行结果是什么 为什么
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```
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var person1 = {
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fullName: function() {
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return this.firstName + " " + this.lastName;
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}
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}
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var person2 = {
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firstName:"John",
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lastName: "Doe",
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}
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person1.fullName.call(person2);
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```
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11. 下面代码的执行结果是什么 为什么
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```
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function speak(){
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var name = this.name
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console.log(`Hello I am ${name}`)
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}
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var me = {
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name: 'a',
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speak: speak
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}
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var you = {
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name: 'b',
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speak: speak
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}
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me.speak()
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you.speak()
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```
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12. 下面代码的执行结果是什么 为什么
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```
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function fn(){
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console.log(this.name)
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}
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fn.name = 'xxx'
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fn()
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```
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13. 下面代码的执行结果是什么 为什么
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```
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function foo() {
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var a = 2;
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this.bar();
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}
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function bar() {
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console.log( this.a );
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}
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foo();
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```
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14. 下面代码的执行结果是什么 为什么
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```
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function foo(){
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console.log(this.a)
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}
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var a = 2
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foo()
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```
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15. 下面代码的执行结果是什么 为什么
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```
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function foo() {
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console.log( this.a );
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}
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var obj = {
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a: 2,
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foo: foo
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};
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obj.foo();
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```
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14. 下面的fn中的this指向谁
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```
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obj1.obj2.obj3.fn()
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```
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15. 下面代码的执行结果是什么 为什么
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```
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function foo() {
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console.log( this.a );
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}
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var obj = {
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a: 2,
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foo: foo
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};
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var bar = obj.foo; // 函数别名!
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var a = "xxxxx"
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bar();
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```
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16. 下面代码的执行结果是什么 为什么
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```
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function foo() {
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console.log( this.a );
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}
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var obj = {
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a: 2,
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foo: foo
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};
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var a = "xxxxx"
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setTimeout( obj.foo ,100);
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```
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17. 下面代码的执行结果是什么 为什么
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```
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function foo(something) {
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console.log( this.a, something );
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return this.a + something;
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}
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function bind(fn, obj) {
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return function() {
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return fn.apply( obj, arguments );
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};
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}
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var obj = {
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a:2
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};
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var bar = bind( foo, obj );
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var b = bar( 3 ); // 2 3
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console.log( b );
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```
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18. 下面代码的执行结果是什么 为什么
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```
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const test = {
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prop: 42,
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func: function() {
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return this.prop;
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},
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};
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console.log(test.func());
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```
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19. 下面代码的执行结果是什么 为什么
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```
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console.log(this === window);
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a = 37;
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console.log(window.a);
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this.b = "MND";
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console.log(window.b)
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console.log(b)
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```
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20. 下面代码的执行结果是什么 为什么
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```
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function f1(){
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return this;
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}
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//在浏览器中：
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f1() === window; //在浏览器中，全局对象是window
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//在Node中：
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f1() === globalThis;
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```
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21. 下面代码的执行结果是什么 为什么
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```
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function f2(){
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"use strict"; // 这里是严格模式
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return this;
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}
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f2() === undefined;
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```
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22. 下面代码的执行结果是什么 为什么
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```
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var obj = {a: 'Custom'};
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var a = 'Global';
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function whatsThis() {
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return this.a;
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}
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whatsThis();
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whatsThis.call(obj);
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whatsThis.apply(obj);
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```
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23. 下面代码的执行结果是什么 为什么
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```
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function C(){
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this.a = 37;
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}
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var o = new C();
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console.log(o.a);
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function C2(){
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this.a = 37;
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return {a:38};
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}
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o = new C2();
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console.log(o.a);
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```
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24. 下面代码的执行结果是什么 为什么
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```
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<button onclick="alert(this.tagName.toLowerCase());">
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Show this
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</button>
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``` |