题目1：下面的代码输出多少？修改代码让fnArri 输出 i。使用两种以上的方法
var fnArr = [];
for (var i = 0; i < 10; i ++) {
fnArr[i] = function(){
return i;
};
}
//输出10，执行的时候i等于10，所以整个数组元素执行后都会是10
console.log( fnArr[3]() );
作用域链：
globalContext = {
AO:{
fnArr:[function1,function2,...,function10]
i:10
function1:
function2:
...
function10:
}
scope:null
}
function1.[[scope]] = globalContext.AO;
function2.[[scope]] = globalContext.AO;
function1Context = {
AO:{
}
scope:function1.[[scope]];//globalContext.AO;
}
function2Context = {
AO:{
}
scope:function2.[[scope]];//globalContext.AO;
}
法一：
var fnArr = [];
for (var i = 0; i < 10; i ++) {
(function(i){
fnArr[i] = function(){
return i;
}
})(i);
}
console.log( fnArr[3]() ); //3
作用域链：
globalContext = {
AO:{
fnArr:[function11,function22,...,function1010]
i:
function1:
function2:
...
function10:
}
scope:null
}
function1.[[scope]] = globalContext.AO;
function2.[[scope]] = globalContext.AO;
function1Context = {
AO:{
i:0;
function11:
}
scope:function1.[[scope]];//globalContext.AO;
}
function11.[[scope]] = function1Context.AO;
function11Context = {
AO:{
}
scope:function11.[[scope]];//function1Context.AO;
}
function2Context = {
AO:{
i:1;
function22:
}
scope:function2.[[scope]];//globalContext.AO;
}
function22.[[scope]] = function2Context.AO;
function22Context = {
AO:{
}
scope:function22.[[scope]];//function2Context.AO;
}
法二：
var fnArr = [];
for (var i = 0; i < 10; i ++) {
fnArr[i] = (function(i){
//IIFE & 闭包
return function(){
return i;
}
})(i);
}
console.log( fnArr[3]() ); //3
作用域链：
globalContext = {
AO:{
fnArr:[function1,function2,...,function10]
i:
function1:
function2:
...
function10:
}
scope:null
}
function1.[[scope]] = globalContext.AO;
function2.[[scope]] = globalContext.AO;
function1Context = {
AO:{
i:0;
function11:
}
scope:function1.[[scope]];//globalContext.AO;
}
function11.[[scope]] = function1Context.AO;
function11Context = {
AO:{
}
scope:function11.[[scope]];//function1Context.AO;
}
function2Context = {
AO:{
i:1;
function22:
}
scope:function2.[[scope]];//globalContext.AO;
}
function22.[[scope]] = function2Context.AO;
function22Context = {
AO:{
}
scope:function22.[[scope]];//function2Context.AO;
}
法三：
var fnArr = [];
for (let i = 0; i < 10; i ++) {
//使用ES6： let
fnArr[i] = function(){
return i;
};
}
console.log( fnArr[3]() );
题目2：封装一个汽车对象，可以通过如下方式获取汽车状态
var Car = (function () {
let speed = 0;
function setSpeed(s){
return speed = s;
}
function getSpeed(){
return speed;
}
function accelerate(){
return speed+=10;
}
function decelerate(){
//速度不能为负数
return speed>0?speed-=10:speed;
}
function getStatus(){
return speed>0?'running':'stop';
}
return {
"setSpeed" : setSpeed,
"getSpeed" : getSpeed,
"accelerate" : accelerate,
"decelerate" : decelerate,
"getStatus" : getStatus
}
})();
Car.setSpeed(30);
Car.getSpeed(); //30
Car.accelerate();
Car.getSpeed();//40;
Car.decelerate();
Car.decelerate();
Car.getSpeed(); //20
Car.getStatus(); // 'running';
Car.decelerate();
Car.decelerate();
Car.getStatus(); //'stop';
//Car.speed; //error
代码：
var Car = {
speed:0,
setSpeed:function(s){
return speed = s;
},
getSpeed:function(){
return speed;
},
accelerate:function(){
return speed+=10;
},
decelerate:function(){ //速度不能为负数
return speed>0?speed-=10:speed;
},
getStatus:function(){
return speed>0?'running':'stop';
},
};
题目3：下面这段代码输出结果是? 为什么?
var a = 1;
setTimeout(function(){
a = 2;
console.log(a);//2
}, 0); //参数为0，被放入执行队列的最后
var a ;
console.log(a); //1
a = 3;
console.log(a); //3
结果：1，3，2
题目4：下面这段代码输出结果是? 为什么?
var flag = true;
setTimeout(function(){
//等待所有任务结束后执行
flag = false;
},0)
while(flag){} //setTimeout会等待它执行完毕，此时flag永远是true，无限循环。
console.log(flag); //不会执行
题目5：下面这段代码输出？如何输出delayer: 0, delayer:1...
（使用闭包来实现）
for(var i=0;i<5;i++){
(function(t){
//参数变量提升 let t;
return setTimeout(function(){
console.log('delayer:' + t );
}, 0);
})(i);
console.log(i);
}```
题目6： 如何获取元素的真实宽高？
function trueStyle(element,pseduoElement){
//IE不支持window.getComputedStyle()，支持element.currentStyle();
return element.currentStyle ? element.currentStyle : window.getComputedStyle(element,pseduoElement);
}
let trueWidth = trueStyle(element).width;
let trueHeight = trueStyle(element).height;
题目7：URL 如何编码解码？为什么要编码？
let myURL = 'https://www.google.com/#q=javascript';
//如果我们想编码一个URL并且可以使用它（访问），使用encodeURI();
let simpleURL = encodeURI(myURL); //"https://www.google.com/#q=javascript"
//如果我们想编码一个URL并且可以将其放置在某URL的参数中，使用encodeURIComponent();
let completeURL = encodeURIComponent(myURL);
let newURL = 'https://www.google.com/?back=' + completeURL;
//"https://www.google.com/?back=https%3A%2F%2Fwww.google.com%2F%23q%3Djavascript"
window.open(simpleURL); //将会打开一个窗口，地址为https://www.google.com/#q=javascript
题目8：补全如下函数，判断用户的浏览器类型
function isAndroid(){
return /Android/.test(navigator.userAgent);
}
function isIphone(){
return /iPhone/.test(navigator.userAgent);
}
function isIpad(){
return /iPad/.test(navigator.userAgent);
}
function isIOS(){
return /(iPad)|(iPhone)/i.test(navigator.userAgent);
}
