JavaScript in usage Introduction

<! DOCTYPE html>//for-in are typically used to traverse an object, or to iterate over an array        //var obj = {        //Name: "Xiaoming",        //Age:8        // };        //For (var k in obj) {        ////Use the dot operator here, you cannot get to the corresponding value:        ////. Role: Access the properties of an object        //Console.log ("key is:" + K + ", value is:" + obj[k]);        // }        //var arr = [1, 3, 5];        //For (var k in arr) {        //Console.log ("key is:" + K + ", value is:" + arr[k]);        // }        //In operator function:        //is to determine whether the property exists in the object, and if so, the return value is: True        //If it does not exist: false        //syntax: Properties in Object        //var obj = {        //name1: "Jack",        //Age:9,        //abc:undefined        // };        //for Name, Note: Window has the Name property        //Console.log ("name1" in obj);//True        //Console.log ("age" in obj);        //Console.log ("age123" in obj);        //if the member exists in the object or is a member of the prototype, the result returned is true        //Console.log ("toString" in obj);        //Console.log (obj.tostring ());        //Console.log ("abc" in obj);        //The in operator determines the array        //for arrays, the index number is the attribute        vararr = [1]; //Console.log ("1" in arr);//False        //Console.log ("0" in arr);//True        //console.log (0 in arr);//True        //to access the members of an array:        //You can use an array index or you can use a stringConsole.log (arr[0]); Console.log (arr["0"]); </script></body>
JavaScript in usage Introduction