Front-end JavaScript Knowledge (iii)

• function memory, judgment is not prime.

  方法一:function isPrime1(n){    if(n<=3){return true}    else{      for(var i=2;i<Math.sqrt(n);i++){        if(n%i==0){return false;}      }      return true;    }};方法二:hash  var isPrime2=(function(){//hash    var hash={};    return function(n){      if(n<=3){return true}      else if(hash[n]!==undefined){        return hash[n];      }else{        for(var i=2;i<Math.sqrt(n);i++){          if(n%i==0){return hash[n]=false}        }        return hash[n]=true;      }    }})();

• array de-

    method One: Var arr1=[1,2,3,2,1,2]; function Repeat1 (arr) {for (Var i=0,arr2=[];i<arr.length;i++) {if (Arr2.indexof (Arr[i]) ==-1) {Arr2.push (AR      R[i]); }}//(traversal end) return arr2;} Method Two: Hashfunction repeat2 (arr) {//iterates through each element in arr, while declaring that hash for (Var i=0,hash={};i<arr.length;i++) {//hash contains the value of the current element      Build//If not included, add a new element to the hash, with the current element value of Key,value default to 1 if (hash[arr[i]]===undefined) {hash[arr[i]]=1;    }}//(traversal end)//convert hash to index: Var i=0;    var arr2=[];    For (arr2[i++] in hash); return arr2;} Method Three: Function Repeat3 (arr) {return Arr.sort (). Join (",,"). Replace (/(^|,,) ([^,]+) (  ,, \2) */g, "$1$2"). Split (",,"); }console.log (REPEAT3 (arr1));  

• Insert Sort

    var arr=[2,4,1,5,3]; function Insertsort (arr) {//traverse each element in arr (I starting from 1) for (Var i=1;i<arr.length;i++) {//To save the current element temporarily in the variable t var t=arr      [i]; var p=i-1;//declares the variable p=i-1//loop: (arr[p]>t&&p>=0) {while (arr[p]>t&&p>=0) {//) assigns the value of P position to        P+1 position arr[p+1]=arr[p]; p--;//p--}//(Loop end) arr[p+1]=t;//Place T in p+1 position}//(Loop End)} insertsort (arr); Console.log (String (arr));  

• Quick sort:

    function quickSort(arr){    //如果arr的length<=1    if(arr.length<=1){      return arr;//就直接返回arr    }    //计算参照位p    var p=Math.floor(arr.length/2);    var left=[];    var right=[];    //删除p位置的元素    var center=arr.splice(p,1)[0];    //遍历arr中每个元素    for(var i=0;i<arr.length;i++){      if(arr[i]>=center){        right.push(arr[i]);      }else{        left.push(arr[i]);      }    }    return quickSort(left) .concat(center,quickSort(right))  }  var sortedArr=quickSort(arr);  console.log(String(sortedArr));

• Regular expressions

  (1) "ryan5 is6 not7 a8 good9 man10"var n=5;var str="ryan is not a good man";str=str.replace(/\b[a-z]+\b/g,function(kw){ return kw+n++;});console.log(str);

• the number of occurrences of each character in the statistics string is the most frequently seen?

    var str= "HelloWorld"; Method One: Use hash for (Var i=0,hash={};i<str.length;i++) {if (Hash[str[i]]) {hash[str[i]]++}else{hash[str[i]]=    1; }} console.dir (hash); method two: Use regular var arr=str.split (""). Sort (). Join (""). Match (/([A-z]) \1*/g). Sort (function (b) {retur n B.length-a.length;  }) Console.log ("Most appears:" +arr[0][0] + "Total" +arr[0].length+ "times"); var hash={};  Arr.foreach (function (val) {hash[val[0]]=val.length;  }); Console.dir (hash);  

• Array Dimension Reduction

  var arr=[    [0,0,0,0],    [0,0,0,0],    [0,0,0,0],    [0,0,0,0],  ];  //method 1:  for(var r=0,arr1=[];r<arr.length;r++){    for(var c=0;c<arr[r].length;c++){      arr1.push(arr[r][c]);    }  }  console.dir(arr1);  //method 2:   for(var r=0,arr2=[];r<arr.length;r++){    arr2=arr2.concat(arr[r]);  }  console.dir(arr2);//method 3:  var arr2=[].concat.apply([],arr);  console.dir(arr2);

• function Assignment

    var f=function(){var a=b=1;}  f();  console.log(b);//1  console.log(a);//报错  var f=function(){var a=b=1;}  setTimeout(f,0);  console.log(b);//报错  f();  var a,b=0, fn=function(){var a=b=2;}  fn();  console.log(a);//undefined  console.log(b);//2

• function currying (Coliward)

    var getN;  function add(n){    getN=function(){console.log(n);}    return function(m){      n+=m;    arguments.callee.toString=function(){        return n;      }      return arguments.callee;    }  }  add(1)(2)(3); getN();//6  add(1)(2)(3)(4); getN();//10  alert(add(1)(2)(3));//6  alert(add(1)(2)(3)(4));//10

• Recursive

  var emp={ work:function(){//3,2,1  var  sum=0;//+3+2+1 +2+1  +1  for(vari=0; i<arguments.length&&arguments[0]>0;        i++){        sum+=arguments[i]            +arguments.callee(              --arguments[i]            );      }      return sum;    }  }  console.log(emp.work(3,2,1));//10

• Closed Package

  （1）function fun(n,o){//外层函数    console.log(o);    return {      fun:function(m){//内层函数 n        return fun(m,n);      }    }  }  var a=fun(0);a.fun(1); a.fun(2); a.fun(3);   //undefined  0      0       0var a=fun(0).fun(1).fun(2).fun(3);//undefined   0    1    2var a=fun(0).fun(1); a.fun(2); a.fun(3);//undefined  0       1      1（2）var a=0,b=0;  function A(a){    A=function(b){alert(a+b++)};    alert(a);  }  A(1);//1  A(12);//13

• Oop

  (1) window.a=300;    function fn1 () {this.a=100;    this.b=200; return function () {alert (THIS.A)}.call (arguments[0])} function fn2 () {this.a=new fn1 ();} var a=new fn1 (). B;//300var v=new fn1 (fn2 ());//[object Object] (2) var Number=2;//4 8 var obj={number:4,//8 fn1: (Fun      Ction () {//var number; this.number*=2;number*=2;      Declare undefined var number=3 in advance;        return function () {this.number*=2;        number*=3;      alert (number);  }}) ()} var fn1=obj.fn1; alert (number); FN1 ();   Obj.fn1 (); 4 9 Alert (window.number),//8 alert (obj.number),//8 (3) 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);}; Foo.getname ();//2getname ();//4foo (). GetName ();//1getname ();//1new foo.getname ();//2new Foo (). GetName ();//3new New Foo (). GetName ();//3 (4) var a=1;var b={A: 2, B:function () {console.log (THIS.A);//1} (), F:this.f=function () {console.log (THIS.A); }};function f () {Console.log (3);} f ();//1b.f ();//2 (B.F) ();//2 (0,B.F) ();//1 (5) var foo=function () {console.log (THIS.A);} var obj={a:2,foo:foo};var a=10;var Bar=obj.foo;var bar2=foo.bind (obj); bar ();//10bar2 ();//2foo ();//10obj.foo ();// 2setTimeout (bar,0);//10 (6) function MyObj () {this.p.pid++;} myobj.prototype.p={"pid": 0}//2myobj.prototype.getnum=function (num) {return this.p.pid+num;} var _obj1=new MyObj (); Create new object, inherit prototype Pid+1var _obj2=new MYOBJ (); Create new object, inherit prototype Pid+2console.log (_obj1.getnum (1) +_obj2.getnum (2));//7 2+1 +

• There are five ways to determine if an object is not an array type:

  (1) typeof cannot judge only the values and functions of the original type (2) isprototypeof judge the parent and object can check the entire prototype chain//may inherit from the array Console.log (ARRAY.PROTOTYPE.ISPROTOTYPEOF ([]) ?"  is an array ":" Not an array "); Console.log (Array.prototype.isPrototypeOf ({})? "  is an array ":" Not an array "); Console.log (Array.prototype.isPrototypeOf () (function () {})? "  Array ":" is not an array ");(3) constructor check the constructor of the specified object to check the entire prototype chain//may inherit from the array var father={};  var son={};  Father.__proto__=array.prototype;  Son.__proto__=father; Console.log (Son.contructor==array? ") is the array ":" Not an array ") Console.log ({}.contructor==array?").  is an array ":" Not an array "); Console.log (function () {}.contructor==array? ")  is an array ":" is not an array ");(4) instanceof checks whether an object is an instance of a constructor that can check the entire prototype chain//may inherit from the array var father={};  var son={};  Father.__proto__=array.prototype;  Son.__proto__=father; Console.log (son instanceof Array? ")  is an array ":" Not an array "); Console.log ({} instanceof Array? "  is an array ":" Not an array "); Console.log (function () {} instanceof Array? "       is an array ":" is not an array ");(5) Forcibly use the object to be checked, calling the original ToString method without checking the entire prototype chain//[object class]: Class-array Date object//Can only check the object that was originally created by the array. Console.log (Object.prototype.toStRing.call ([]) = = "[Object Array]"? "      is an array ":" Not an array ");      Console.log (Object.prototype.toString.call ({}));      Console.log (Object.prototype.toString.call () (function () {}));      Console.log (Object.prototype.toString.call (/\d/));       var father={};       var son={};       Father.__proto__=array.prototype;      Son.__proto__=father; Console.log (Object.prototype.toString.call (son) = = "[Object Array]"? " is an array ":" is not an array ");//is not A//conclusion: Once an object is created, the class property cannot modify/modify the inheritance relationship or modify the Class Property (6) Array.isarray (obj) does not check the entire prototype chain CO      Nsole.log (Array.isarray ([]));  Console.log (Array.isarray ({})); If the browser does not support IsArray if (array.prototype.isarray===undefined) {//if (! Array.isarray)//give? Add IsArray Method Array.prototype.isarray=function (ARG) {//forcibly call the original ToString method, and "[Object Arra Y] "compare return Object.prototype.toString.call (arg) = =" [Object Array] "?"      is the array ":" is not an array "; }  }

• Custom Object.create ()--Handwriting

    Object.create=function(father,props){      console.log("我的create");      /*使用setPrototypeOf方法      var o=Object();//1. 创建空对象      Object.setPrototypeOf(o,father);//2. 继承father      */      /*不使用setPrototypeOf方法      function Constructor(){}      Constructor.prototype=father;      var o=new Constructor();      */      Object.defineProperties(o,props);//3. 定义新属性      return o;  }

• Principles of deep cloning

  Object.clone=function(obj){//深克隆if(typeof(obj)=="object"){//如果obj是对象  var o=//有必要区分数组和普通对象  Object.prototype.toString.call(obj)=="[object Array]"?[]:{};      for(var key in obj){//遍历obj的自有属性          //如果key是obj的自有属性          if(obj.hasOwnProperty(key)){              o[key]=arguments.callee(obj[key]);//arguments.callee调的是当前的Object.clone函数              }      }      return o;      }else{//如果obj是原始类型的值，就直接返回副本          return obj;      }  }

• If the browser does not support the Every property, the every implementation principle

    if(Array.prototype.every===undefined){     Array.prototype.every=function(fun){      //遍历当前数组中每个元素      for(var i=0;i<this.length;i++){          if(this[i]!==undefined){//调用fun,依次传入当前元素值,位置i,当前数组作为参数  ，将返回值，保存在变量r中          var r=fun(this[i],i,this);          if(r==false){//如果r为false             return false;//返回false          }          }           }//(遍历结束)       return true;//返回true     }  }

• If the browser does not support the some property, the some implementation principle

    if(Array.prototype.some===undefined){     Array.prototype.some=function(fun){        for(var i=0;i<this.length;i++){        if(this[i]!==unefined){          var r=fun(this[i],i,this);              if(r==true){ return true; }                }            }        return false;     }      }

• The browser does not support the map attribute, the map implementation principle

    if(Array.prototype.map===undefined){     Array.prototype.map=function(fun){      //创建空数组: newArr      var newArr=[];      //遍历当前数组中每个元素      for(var i=0;i<this.length;i++){         //如果当前元素不是undefined         if(this[i]!==undefined){//判断稀疏数组//调用fun传入当前元素值，位置i，当前数组，将结果保存在r中              //将newArr的i位置赋值为r          var r=fun(this[i],i,this);                  newArr[i]=r;         }      }//(遍历结束)      return newArr;//返回newArr     }  }

• If the browser does not support the reduce attribute, the implementation principle of reduce

    if(Array.prototype.reduce===undefined){     Array.prototype.reduce=function(fun,base){       base===undefined&&(base=0);       for(var i=0;i<this.length;i++){      if(this[i]!==undefined){         base=fun(base,this[i],i,this);      }           }       return base;         }  }

• If the browser does not support the bind attribute, the implementation principle of the BIND function

       if(Function.prototype.bind===undefined){     Function.prototype.bind=function(obj/*，参数列表*/){      var fun=this;//留住this              //*****将类数组对象，转化为普通数组      var args=Array.prototype.slice.call(arguments,1);      //args保存的就是提前绑定的参数列表      /*function slice(1){         var sub=[];         for(var i=0;i<length;i++){          sub.push(arguments[i]);         }         return sub;      }*/      return function(){                 //将后传入的参数值，转为普通数组               var innerArgs=Array.prototype.slice.call(arguments);//将之前绑定的参数值和新传入的参数值，拼接为完整参数之列表         var allArgs=args.concat(innerArgs)        //调用原始函数fun，替换this为obj，传入所有参数        fun.apply(obj,allArgs);      }     }  }

Front-end JavaScript Knowledge (iii)