JS筆試彙總

//console.log(a[b]);
var a={};
var b={key:'b'};
var c={key:'c'};
a[b] = 456;
a[c] = 123;
console.log(a[b]); //"123"
console.log(a[c]); //"123"

 

var obj1 = {x: 1};
var num1 = 1;
var arr1 = [obj1, num1];
obj1 = {x: 2};
num1 = 2;
console.log(arr1[0].x, arr1[1]);// 1 1

var arr2 = arr1;
obj1.x = 3;
arr1[1] = 3;
console.log(arr2[0].x, arr2[1])//1 3

 

Promise.resolve().then(() => {
    console.log(1);
    return Promise.reject();
}).catch(()=>{
    console.log(2);
}).catch(()=>{
    console.log(3);
}).then(()=>{
    console.log(4);
})
// 1 2 4

 

//
(function(x) {
    return (function(y) {
        console.log(x);
    })(1);
})(2);//"2"

 

//閉包的應用
for(var i=0;i<5;i++){
    setTimeout(function(){
        console.log(i);
    },1000*i);
}//->5 5 5 5 5

for(var i=1;i<=5;i++){
    (function(j){
        setTimeout(function(){
            console.log(j);
        },1000*j);
    })(i);
}//->1 2 3 4 5

for(var i=1;i<=5;i++){
    (function(i){ setTimeout(function(){ console.log(i); },1000); })(i); }//->1 2 3 4 5

for(var i=1;i<=5;i++){
    setTimeout(function(i){
        console.log(i);
    },1000*i,i);
}//->1 2 3 4 5

for(let i=1;i<=5;i++){
    setTimeout(function(){
        console.log(i);
    },1000*i);
}//->1 2 3 4 5

 

var fn = function() {
    var c = "bbb";
    return {
        a: function(){
            return c;
        },
        b: function(d) {
            c = d;
        }
    }
}();
console.log(fn.a());//bbb
console.log(fn.b('ccc'));//undefined
console.log(fn.c);//undefined

 

var out = (function(x){
    delete x;
    return x;
})(0);
console.log(out);//0

var x=1;
var out = (function(){
    delete x;
    return x;
})();
console.log(out);//1

//
if(10>9>8==true) {
    console.log('html');
}else{
    console.log('css');
}//css

//
var len =0;
function f(){
    console.log(this.len);
}
var obj = {
    len:5,
    met: function(f){
        f();
    }
};
obj.met(f,1);//0

//
const data = {};
data===1;//false
data=1;//TypeError
data.size=100;//100

//
function foo() {
    let p;
    for(let i=0;i<3;i++){//let聲明的i只在塊級做用域中有效
        if(i==2){
            p = function(){//返回值給了外部變量p=2；
                return i;
            }
        }
    }
    console.log(p());//取值是2而不是3；
    console.log(i);//1
}
foo();//2

//
function foo() {
    let p;
    for(var i=0;i<3;i++){//var 聲明的變量全局有效
        if(i==2){
            p = function(){
                return i;//全局的i決定let聲明的變量p
            }
        }
    }
    console.log(p());//3
    console.log(i);//3
}
foo();

//對象調用方法時老是先從實例中尋找，而後再向原型對象中查找
function A(){
    this.fn = function(){
        return 1;
    }
}
A.prototype.fn = function(){return 2};
var a = new A();
a.fn();//1

//
function Foo(){
    var i=0;
    return function(){
        console.log(i++);
    }
}
var f1 = Foo();
var f2 = Foo();
f1();//0
f2();//0

//
function f1(){
    var a = 10;
    if(a>5){
        var b = 7;
    }
    console.log(b);
}
function f2(){
    var a = 10;
    if(a>5){
        const b = 7;
    }
    console.log(b);
}
f1();//7
f2();//ReferenceError: b is not defined

//
var foo = {
    x:1
};
function bar() {
    console.log(this.x);
}
bar.apply(foo);//1
bar.call(foo);//1
bar.bind(foo)();//1

//重寫bind
Function.prototype._bind = function(ctx){
    var that=this;
    return function(){
        return that.apply(ctx, arguments);
    };
}
bar._bind(foo)();//1

//
var F = function(){};
Object.prototype.a = function(){}
Function.prototype.b = function(){};
var f = new F();
'a' in f;//true
'a' in F;//true
'b' in f;//false
'b' in F;//true

//
var obj1 = {
    x:1
}
var obj2 = Object.create(obj1);
obj1===obj2.__proto__;//true
obj1.hasOwnProperty('x');//true
obj2.hasOwnProperty('x');//false
obj1.x===obj2.x;//true

//
const a = /123/gi;
const b = /123/gi;
console.log(a==b);//false
console.log(a===b);//false

 

var t1 = new Date('2018-07-02');//Mon Jul 02 2018 08:00:00 GMT+0800 (中國標準時間)
var t2 = new Date(2018,07,02);//Thu Aug 02 2018 00:00:00 GMT+0800 (中國標準時間)
t1.getDay();//1
t2.getDay();//4
t1.getMonth();//6
t2.getMonth()//7
t1.getDate();//2
t2.getDate();//2
t1.getTime();//毫秒數
t2.getTime();
t1.getHours();
t1.getMinutes();
t1.getSeconds();

 

//變量提高
function baidu() {
    console.log(val);
    var val = 'b';
    console.log(val);
}
baidu();// undefined   b

(function(){
    var a = b = 100;
})();
typeof a;//undefined (不能訪問私有做用域中的變量)
typeof b;//number (b沒有指定類型，自動變爲全局變量)
//函數提高與變量提高
console.log(typeof a);
function a(){};
var a;// function

com(10,100);//執行函數提高後的最後一個函數
var com = function(a,b){//函數表達式不會被提高
    console.info(a*b);
}
function com(a,b) {//函數聲明被提高到頂部
    console.info(a+b);
}
function com(){//函數聲明被提高到頂部
    console.info((a+b)*2);
}
com(2，10);執行函數表達式；
// 220 20

 

//trim實現去除首尾空格
function trim(str){ 
    return str.replace(/(^\s*)|(\s*$)/g, ""); 
}
trim(" a bc de   ");//"a bc de"

"1.2.3".split('') //的等價方法 
"1.2.3".split(/(\.)/);

var s1 = new String('fe');
var s2 = new String('fe');
console.log(s1==s2)//false
console.log(s1===s2)//false

var foo = 10+'20'-10//1010
console.log("   AB"<"   CD")//true

 

 

//函數長度
(function(a,b,c){}).length;//3
(function(a,b,c=3){}).length;//2
(function(a=1,b,c){}).length;//0
(function(a,b=2,c){}).length;//1

 

//打印數組中重複元素
function dedupe(array) {
    var newArr = [];
    var no =[];
    for(var i=0; i<array.length; i++) {
        if(newArr.indexOf(array[i]) == -1) {
            newArr.push(array[i]);
        } else {
            no.push(array[i]);
        }
    }
    return no;
}
var arr = [1, 1, 2, 3, 4, 5, 5];
console.log(dedupe(arr));//[1, 2, 3]

const timeout = ms => new Promise((resolve, reject) => {
    setTimeout(() => {
    resolve();
}, ms);
});

const ajax1 = () => timeout(2000).then(() => {
    console.log('1');
    return 1;
});

const ajax2 = () => timeout(1000).then(() => {
    console.log('2');
    return 2;
});

const ajax3 = () => timeout(2000).then(() => {
    console.log('3');
    return 3;
});

const mergePromise = ajaxArray => {
// 在這裏實現你的代碼
    var data=[];
    var res = Promise.resolve();
    ajaxArray.forEach(function(item){
        res = res.then(item).then(function(ref) {
            data.push(ref);
            return data;
        });
    });
    return res;
};

mergePromise([ajax1,ajax2,ajax3]).then(data => {
    console.log('done');
    console.log(data);
});
//
  //1
  //2
  //3
  //done
  //[1,2,3]

//重寫 console.log()
//1.
console.log = (function(self) {
    return function(){
        var args = Array.prototype.slice.call(arguments, 0);
        self.apply(console, args);
    }
})(console.log);
//2.
var log = console.log;
console.log = function(text) {
    var args = Array.prototype.slice.call(arguments, 0);
    log.apply(console, args);
};
console.log([1,2,3,[1,2,3]]);

 

//重寫indexOf
Array.prototype.indexOf = function(searchElement){
    var index,
        _arguments = this,
        args = Array.prototype.slice.call(_arguments),
        count=0;
    for(var x in args){
        if(args[x] === searchElement)
        {
            index = x;
            count=1;
            break;
        }
    }
    if(!count)
        return -1;
    return index;
};
var arr = [1,2,3,4,5,6];
var index = arr.indexOf(6);
console.log(index);

 

// wrap: 3
// arr: [1,2,3,4,5,6,7,8]
// output: 7 8 4 5 6 1 2 3

function flatten(arr) {
    var res = [];
    for(var item of arr){
        if(Array.isArray(item)){
            var child = flatten(item);
            //res = res.concat(child);
            res.push(...child);
        }
        else
            res.push(item);
    }
    return res;
}
function groupOutput(wrap, arr) {
    var newarr=[], len = arr.length;
    for(var i=0;i<len; i=i+wrap){
        var args = arr.slice(i,i+wrap);
        newarr.push(args);
    }
    newarr.reverse();
    return flatten(newarr);
}
var res = groupOutput(5,[1,2,3,4,5,6,7,8]);
console.log(res);

 

//使instanceof判斷某個對象是不是數組時返回false
//instanceof操做符有一個問題就是，它假定只有一個全局做用域。
//若是一個網頁中有多個框架（iframe元素），那實際上就存在兩個以上不一樣的全局執行環境，從而存在兩個以上不一樣版本的Array構造函數。
//若是你從一個框架向另外一個框架傳入一個數組，那麼傳入的數組與在第二個框架中原生建立的數組分別具備各自不一樣的構造函數。
//傳入的數組在該框架中用instanceof操做符判斷就會返回false。
var frame=document.createElement("iframe");//建立一個框架
document.body.appendChild(frame);
var c=window.frames[0].Array;//取得框架全局執行環境中的Array構造函數
var d=new c();//在框架全局執行環境中建立一個數組d
console.log(d instanceof Array);//在當前頁面的執行環境中用instanceof操做符判斷d是否爲數組，返回false
console.log(Array.isArray(d));//true

  

//獲取兩個時間相差的小時數
function getHour(t1,t2){
    var res;
    //判斷日期格式是不是正確的
    if(!(isNaN(t1)&&!isNaN(Date.parse(t1)))||!(isNaN(t2)&&!isNaN(Date.parse(t2)))){
    console.log('0');
    return;
    }
    t1 = new Date(t1.replace(/-/g, '/'));
    t2 = new Date(t2.replace(/-/g, '/'));
    var ms = Math.abs(t1.getTime()-t2.getTime());
    var hour = Math.floor(ms/1000/60/60);
    var min = Math.floor(ms/1000/60);
    if(min%60>=0&&min%60<=29)
        res = hour;
    else
        res = hour+0.5;
    console.log(res);
}
getHour('2018-9-15 13:13','2018-9-17 13:45');

 

//順豐筆試
function compare(str, str1) {
    var map = {},res=[],ans;
    var len = str.length,
        len1 = str1.length;
    for(var i=0;i<len;i++){
         if(str1.indexOf(str[i])===-1)
            res.push(str[i]);
    }
    for(var j=0;j<len1;j++){
         if(str.indexOf(str1[j])===-1)
            res.push(str1[j]);
    }
    //去重
    for(var j=0;j<res.length;j++){
         map[res[j]] = res[j];  
    }
    var arr = [];
    for(var key in map){
         arr.push(key);   
    }
    arr.sort();
    var ans = arr.join('') + arr.reverse().join('');
    return ans;
}
compare("afsd", "efrdgg");//"aegrssrgea"

 

//螺旋矩陣
function handler(num1, num2, num3){
    var cnt=1;
    while(num2!=num1 && num3!=num1 && num2>1 && num3>1){
        num2--;num3--;
        cnt+=(4*(num1-1));
        num1-=2;
    }
    var x = 1,y=1;
    var flag = true;
    while(flag && x+1<=num1){if(x===num3 && y===num2){console.log(cnt);flag = false;}else{x++;cnt++;}}
    while(flag && y+1<=num1){if(x===num3 && y===num2){console.log(cnt);flag = false;}else{y++;cnt++;}}
    while(flag && x-1>=1){if(x===num3 && y===num2){console.log(cnt);flag = false;}else{x--;cnt++;}}
    while(flag && y-1>=1){if(x===num3 && y===num2){console.log(cnt);flag = false;}else{y--;cnt++;}}
    if(num1===1) console.log(cnt);
}
handler(4, 3, 3);

//2. 長度爲n的數組分割爲k段，讓完成任務的工期取得最小；