JS in operator, use of foreach and map-basic knowledge Summary------peng kee (016)

In Operator:

<script>/*1. Ability to traverse the properties of an object*/    varobj = {        ' Name ': ' Jack ', Age:20    };  for(varKeyinchObj) {console.log (key+ ":" +obj[key]); }    /*2. You can also determine whether an object can access a property, regardless of whether the property is defined in the current object*/Console.log (' Name 'inchobj);//trueConsole.log (' toString ')inchobj);//trueConsole.log (' toString1 'inchobj);//false</script>

Use of Foreach:

<script>/*foreach is used to iterate over an array*/    //var arr= [123,2,4,35,435,65,7,658,67,98];    /*Value: The current traversal to the element value Index: current element indexed arr: the currently traversed array **/    /*Arr.foreach (function (value,index,arr) {console.log (value + ":" + index + ":" + arr); })*/    /*Customizing the foreach function*/Array.prototype.myForEach=function(callback) { for(varI =0;i<arr.length;i++) {callback ( this[i],i, this); }    }    vararr1= [123,2,4,35,435,65,7,658,67,98]; Arr1.myforeach (function(value,index) {console.log (value+ ":" + index + ":" +arr1); });</script>

Use of Map:

<script>varArr= [123,2,4,35,435,65,7,658,67,98]; /*double the array value and store it in an array*/    /*1. Use the for*/    //var newarr=[];    /*for (var i = 0; i < arr.length; i++) {var obj = arr[i];    Newarr.push (obj*2); } console.log (newArr);*/    /*2. Using the foreach*/    /*Arr.foreach (function (value,index,arr) {newarr.push (value*2);    }); Console.log (newArr);*/    /*3. Using the map function*/    /*arr.map (function (value,index,arr) {newarr.push (value*2);    }); Console.log (newArr);*/    /*Map stores the results in a newly generated array and returns*/   /*var newArr = arr.map (function (value,index,arr) {return value * 2;    }); Console.log (newArr);*/    /*how map is implemented*/Array.prototype.myMap=function(callback) {vartemp = [];  for(vari=0;i< this. length;i++){            varv = Callback ( this[i],i, this); if(v) {temp.push (v); }        }        returntemp;    }; varNEWARR = Arr.mymap (function(value,index,arr) {returnValue * 2;    }); Console.log (newArr);</script>

JS in operator, use of foreach and map-basic knowledge Summary------peng kee (016)