javascript check undefined or null

This article mainly introduces the JavaScript static type check tool FLOW introduction. If you need it, you can refer to the static type check tool developed by Facebook for JavaScript. Its code is hosted on github and complies with the BSD open-source protocol. About Flow It helps us capture Common Errors in

= ' checkbox ']"). Prop ("Checked", "checked");Uncheck:$ ("input[type= ' checkbox ']"). Prop ("checked", false);3. Get Value valuesUse jquery to get the value of the checkbox, and in the case where the value is not given, the value gets "on".When using jquery to get the value of the checkbox, given the value, the obtained value is the value.4. Example: Implementing a reverse selection$ (": CheckBox"). each (function() { if($ (). Prop ("checked")) {$ ( 　　this). Prop ("Checked",false);　　}Else{$ (

Flow is a static type checking tool for JavaScript that is produced by Facebook. Its code is hosted on top of GitHub and is compliant with the BSD open source protocol. About Flow It can help us catch common bugs in JavaScript development without needing to modify your original code, such as static type conversion, null reference, and so on.At the same time, Fl

Check native APIs used in JavaScript and javascriptapi During this time, I doubled the JavaScript api and found a lot of good wheels, saving me trouble.Parses string objects We all know that JavaScript objects can be serialized as JSON or parsed as objects, but the problem is that if something is neither JSON nor objec

The way JavaScript operates a checkbox is similar to how it operates radio, using the checked property of element items. Gets the checkbox element collection, iterates through the collection, and operates on each item in the collection.Here are a few common examples of commonly used checkbox check boxes.Take valueGiven pageTo get the value of a multi-box, what do you do with it?The same steps as getting the

1.jsp Code@ Page Language="Java"ContentType="text/html; Charset=utf-8"pageencoding="UTF-8"%>DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" "Http://www.w3.org/TR/html4/loose.dtd ">HTML>Head>Metahttp-equiv= "Content-type"content= "text/html; charset=utf-8">title>Page no refresh use Ajax to check if the user name is registered (post mode)title>Scripttype= "Text/javascript"> functionCreateajax

Check [pitfalls] in the regular expressions in javascript and brackets in the regular expressions. When using regular expressions in javascript, you need to pay attention to a pitfall in brackets, that is, the metacharacters in brackets. I stepped on the trap myself. I searched the internet and many others stepped on the trap, so I 'd like to explain it. Brackets

Check whether a user has installed a software. I. materials: Function ocxstatus (){ VaR newobj; Try { Newobj = new activexobject ("tvantsx. tvantsxctrl.1 "); If (typeof newobj! = 'Undefined '){ Newobj = NULL; Return true; } } Catch (e ){ Newobj = NULL; Return false; } } Ii. Problems: The yellow backgro

Check Properties var mouse = { "name": "Betta", "age": 3, "varieties": "Milaoshu" } Mouse.hasownproperty ("name"); True mouse.hasownproperty ("sex");//false Add properties Defines an object dog, then assigns a variety of attributes, then gives the color attribute, and finally traverses all attributes and values var dog={ name: "Mango", type: "King of the Will", eat:function () { alert ("Eat"); } object.prototype.color

1 //1. Get the value of a cookie with the specified name objname2 functionGetCookie (objname) {3 varArrstr = Document.cookie.split (";");//between the various cookies;4 for(vari=0;i){5 vartemp = arrstr[i].split ("=");//the cookie name and cookie value are separated by =6 if(Temp[0] = =objname)7 returnUnescape (temp[1]);8 } 9 　　 return""; Ten } One A //2. Add a cookie value to the browser's built-in Documnet.cookie object - functionAddcookie (objname,obj