front end
Write about the front-end interview questions you have encountered today
- There is an array a of unknown length. If its length is 0, add the number 1 to the array, otherwise the first element will be dequeued according to the first-in first-out queue rule.
a.length===0?a.push(1):a.shift()
- JS parses the parameters of the url into objects
getUrlKey('http//aaa/txt.php?a=1&b=2&c=3')
function getUrlKey(url){
let params={
}
let urls=url.split('?');
let arr=urls[1].split('&');
for(let i=0;i<arr.length;i++){
let a=arr[i].split('=');
params[a[0]]=a[1]
}
return params;
}
- Output the following console.log
var a = 10;
(function () {
console.log(a);
a = 20;
console.log(window.a);
var a = 30;
console.log(a)
})()
//结果：undefined 10 30
- Output the following console.log
let a = 1;
(function a(){
a = 2;
console.log(a);
})();
console.log(a);
//结果：
ƒ a(){
a = 2;
console.log(a);
}
1
//(function (){})() 是自执行函数
- Write the following result:
function Foo() {
this.a = function () {
console.log(1)
};
Foo.a = function () {
console.log(2)
}
}
Foo.prototype.a = function () {
console.log(3)
};
Foo.a = function () {
console.log(4)
};
Foo.a();
let obj = new Foo();
obj.a();
Foo.a();
// 结果：4 1 2
- Write the following result:
function Foo() {
getName = function () {
alert (1); };
return this;
}
Foo.getName = function () {
alert (2);};
Foo.prototype.getName = function () {
alert (3);};
var getName = function () {
alert (4);};
function getName() {
alert (5);}
//请写出以下输出结果：
Foo.getName();//2
getName();//4
Foo().getName();//1
getName();//1
new Foo.getName();//2
new Foo().getName();//3
new new Foo().getName();//3
- var s="are you ok", write js to become are| you| okay|
function split(){
var str="are you okay",
res=""
var arr=str.trim().split(/\s+/)
for(i=0;i<arr.length;i++){
res+=arr[i]+"| "
}
return res;
}
- Write a sum method that can work normally when called in the following way [curry]
console.log(sum(2,3))// 5
console.log(sum(2)(3))//5
function add() {
// 第一次执行时，定义一个数组专门用来存储所有的参数
var _args = [].slice.call(arguments);
// 在内部声明一个函数，利用闭包的特性保存_args并收集所有的参数值
var _adder = function() {
_args.push(...arguments);
return _adder;
};
// 利用toString隐式转换的特性，当最后执行时隐式转换，并计算最终的值返回
_adder.toString = function () {
return _args.reduce(function (a, b) {
return a + b;
});
};
return _adder;
}
add(2,3);
add(2)(3);
- What does the following expression get?
4+3+2+“1”
答案：“91”
4+3+2-“1”
答案：8
- Are the arguments in the function an array? If not, how to convert it into a real array?
Not an array
function func(){
console.log(arguments);
return [ ].slice.call(arguments);
}
console.log(func(1,2,3))
- What is the output of the following code execution, and clarify the reason
var x=3;
var foo={
x:2,
baz:{
x:1,
bar:function(){
return this.x;
}
}
}
var go=foo.baz.bar;
console.log(go()); //第一个
console.log(foo.baz.bar()); //第二个
this的问题，
首先我们要看第一个，这时this指向的是window
其次看第二个，调用对象是foo.baz
所以这时this指向的是x:1
- What is the output of the following code after execution, and explain the analysis process.
let x=0;
async function test(){
x+=await 2;
console.log(x);
}
test();
x+=1;
console.log(x);
//答案：1 , 2
这里相关的就是同步还是异步
我们程序执行的时候，一般是所有同步的都结束之后，
再执行微任务，然后宏任务
所以asyn 这函数是需要后面执行的