一些被忽略掉的面试题-白红宇

一些被忽略掉的面试题

阅读量：4356 次

发布时间：2019-06-07

本文共 5803 字，大约阅读时间需要 19 分钟。

//indexOf  没有出现返回-1    //split 拆分字符串    function queryURLParameter(url) {        let obj = {};        if (url.indexOf('?') < 0) return obj;        let ary = url.split('?');        url = ary[1];        ary = url.split('&');        for (let i = 0; i < ary.length; i++) {            let cur = ary[i],                curAry = cur.split('=');            obj[curAry[0]] = curAry[1];        }        return obj;    }    //charAt charCodeAt substr subString slice substr    console.log(queryURLParameter('https://www.google.com/search?q=%E5%BC%A0%E4%B8%89'));    //indexOf split charAt slice    function queryURLParameter(url) {        let reg = /([^&?=]+)=([^&?=]+)/g,            obj = {};        url.replace(reg, function () {            obj[arguments[1]] = arguments[2];        });        return obj;    }    String.prototype.myQueryURLParmeter = function () {        let reg = /([^&?+]+)=([^&?+]+)/g;        let obj = {};        this.replace(reg, (...arg) => {            obj[arg[1]] = arg[2];        });        return obj;    };    url.myQueryURLParmeter();    //2    console.log(a); //undefined    var a = 12;    function fn() {        console.log(a); //由于局部作用域a声明了,a=>undefined        var a = 13;    }    fn();    console.log(a); //12    //3    console.log(a); //undefined    var a = 12;    function fn() {        console.log(a); //12        a = 13;    }    fn();    console.log(a); //13    //4    console.log(a); //程序报错后面不执行    a = 12;    function fn() {        console.log(a);        a = 13;    }    fn();    console.log(a);    //5    var foo = 1;    function bar() {        if (!foo) {            var foo = 10;        }        console.log(foo);    }    bar(); //10    //6    //全局下的变量提升 var n;var c; a=地址    var n = 0;    function a() {        //私有作用域:var a;b=地址;        var a = 10;        function b() {            n++;            console.log(n);        }        b();        return b; //地址    }    var c = a(); //11    c();//12    console.log(n);//0    //7    var a = 10, b = 11, c = 12;    function test(a) {        //私有作用域: a=10  var b        a=1; //私有 A=1        var b=2;  //私有b=2        c=3; //全局c=3    }    test(10);    console.log(a, b, c);//10 ,11,3    //8    //变量提升 :var a;=>window.a=undefined=>a in window 为true    if (!("a" in window)) {//条件不成立        var a=1;    }    console.log(a); //undefined    //9    //变量提升: var a; b=地址    var a=4;    function b(x,y,a) {        //=> 私有作用域 : x=1,y=2;a=3        console.log(a);//3        arguments[2]=10;//让第三个传递进来的实参等于10        console.log(a);//10    }    a = b(1, 2, 3);//undefined  因为B函数执行没有返回值    console.log(a);//3,10,undefined    /*    * 在js的非严格模式下,函数的参数集合域形式变量存在"映射"关系    * 不管其中谁改变了,另外一个都跟着改变    * 在js严格模式下,arguments和形参变量的映射关系被切断了    * 互不干扰    * */    //10    //变量提升 var foo;    var foo='hello';    (function (foo) {        //私有作用域 foo='hello'(我们的foo和外面的foo是不同的变量        console.log(foo);//hello        var foo = foo || 'world';        console.log(foo);//hello    })(foo); //把全局Foo的值当做实参传递给私有作用域中的形参    console.log(foo);//hello    /*    * A&&B  A为假返回A,A为真返回B    * A||B  A为真返回A,A为假返回B    * 逻辑与的优先级高于逻辑或    * */    function fn(num,callBack) {        //如果num没有传递至:让其默认值为0        //if(typeOf num==="undefined') num=0;        num=num||0;//ES6可以给形参添加默认值        callBack&&callBack();//符合条件就去执行    }    //11    var a=9;    function fn() {        a=0;        return function (b) {            return b+a++;        }    }    var f=fn();    console.log(f(5));//5 a=1    console.log(fn()(5));//5 fn()=>a=0, a=1    console.log(f(5));//6 a=2    console.log(a);//2    //12    //变量提升 var ary; var res;fn=地址    var ary = [1, 2, 3, 4];    function fn(ary) {        ary[0]=0;        ary=[0];        ary[0]=100;        return ary;    }    var res=fn(ary);    console.log(ary);//[0,2,3,4]    console.log(res);//100

//13function fn(i) {    return function (n) {        console.log(n + (--i));    }}var f=fn(2);f(3); //4  i=1fn(4)(5);//8fn(6)(7);//12f(8);//8  i=0//14var num=10;//60  65var obj={num: 20};//30obj.fn=(function (num) {    this.num=num*3;    num++;//21 22 23    return function (n) {        this.num+=n;        num++;        console.log(num);    }})(obj.num);//自执行函数var fn=obj.fn;fn(5);//22obj.fn(10);// 23console.log(num, obj.num);//65 30//15function Fn() {    this.x=100;    this.y=200;    this.getX=function () {        console.log(this.x);    }}Fn.prototype={    y:400,    getX:function () {        console.log(this.x);    },    getY:function () {        console.log(this.y);    },    sum:function () {        console.log(this.x + this.y);    }};var f1=new Fn;var f2=new Fn;console.log(f1.getX === f2.getX);//false 地址不一样console.log(f1.getY === f2.getY);//true两个的原型是一致的console.log(f1.__proto__.getY === Fn.prototype.getY);//trueconsole.log(f1.__proto__.getX === f2.getX());//falseconsole.log(f1.constructor);//f1私有没有去原型找,Object

//16for(var i=0;i

学东西不要学表面要学原理要学核心

//17var fullName='language';var obj={    fullName:'javascript',    prop:{        getFullName:function(){            return this.fullName;        }    }};console.log(obj.prop.getFullName());//undefined//this=>obj.prop=>obj.prop.getFullName=>undefined//this指向问题 ,方法执行看前面有没有点,点谁,this指向thisvar test=obj.prop.getFullName;console.log(test());//this=>window  language //18    var name='window';    var Tom={        name:"Tom",        show:function () {            console.log(this.name);        },        wait:function () {            var fun=this.show;            fun();        }    };    Tom.wait();//this:Tom=>fun=Tom.show=> fun()  没有点this是window=> 打印'window'

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