null undefined

Although JavaScript is a weakly typed language, it also has several data types of its own, namely number, String, Boolean, Object, udefined, and Null. Where object belongs to a complex data type, object is made up of unordered key-value pairs. The

Learning Catalog One, data type Data type Second, operator Increment and decrement operators: Bitwise operators:Boolean operator:Additive operator:Equality operator Third, the statementFor-in statementLabel statement One, data type Data type

Seems to have seen null==undefined,null!==undefined before, but also has not cared. Recently looked at someone else's program source code, everywhere have some such as if (x!=undefined&&x!=null&&x!= ""), such as judgment, suddenly feel written

The js object and array object are unordered attribute sets, and each attribute has its own name and value. The Code is as follows: /*Array and object [fifth edition of JavaScript authoritative guide]*//*Object: an unordered property set. Each

This article mainly analyzes call, apply, and bind methods in Javascript, and summarizes the connections and differences between call, apply, and bind methods at the end of this article, which has good reference value, let's take a look at it. The

Naming Conventions are necessary to enhance the readability of the Code, so that you can understand what you want to express at a Glance. Standards are rules that make the code easier for later maintenance, it can also greatly improve the

Definition object of object quantity: it is an unordered property set, and each property has its own name and value. It consists of a list of attribute descriptions. Each attribute description is separated by a comma. Each attribute description

It seems that I have also seen null = undefined, null! = Undefined. One of the pastProgramSource code, such as if (X! = Undefined & X! = NULL & X! = "") And so on, suddenly felt that the write is very wordy, I usually directly if (X) {} No matter

The difference and connection caused by undefinednull seems to have been seen before: null = undefined, null! = Undefined. Recently I 've looked at other people's program source code, and there are some such as if (x! = Undefined & x! = Null & x!

1. Selector structure jquery selector can be divided into several blocks according to the source code.Init:function (selector, context, rootjquery) {...HANDLE: $ (""), $ (null), $ (undefined), $ (false)...Handle HTML Stringsif (typeof selector

Introduction This article introduces the JavaScript language to professional programmers. It is a small language. If you are familiar with other programming languages, this article is not that hard to understand. JavaScript is not Java. They are two

Javascript importanceUsage1. In web applications, javascript is used in front-end interface programming;2. Web2.0 and Ajax promote the javascript language.3. As a large number of c/s applications turn to B/s, the rich client technology will be

Chapter III Basic Concepts Everything in ECMAScript (variables, function names, and operators) is case-sensitive. Identifiers are the names of variables, functions, attributes, or parameters of a function. The constituent rules for

Before introducing the differences between the three JS data types, let's take a look at the JS data types. In a language such as Java and C, before using a variable, you must first define the variable and specify its data type, which is an integer,

Shallow copy of an arrayIf it is an array, we can use some of the array's methods such as: Slice, CONCAT returns a new array of attributes to achieve the copy. Like what: var arr = [ " old ", 1 , true , null var new_arr = Arr.concat () ;

Recently has been in the written interview, often encountered such as 123== ' 123 ', ' abc ' ==true and other issues, including the correct answer, there is also wrong, the main reason or the ECMAScript norms did not understand clearly, many of the

&& | | In the jquery source code is particularly widely used, from the Internet to find some examples for reference, the use of it to study a bit:1. &&function A () {Alert ("a");return true;}Function B () {Alert ("B");return true;}var c=a () &&b

Copy Code code as follows: /* Arrays and objects "JavaScript Authority Guide, Fifth Edition" */ /* Object: is a collection of unordered attributes, each with its own name and value. /* Create object Simple method, Object direct

A bad time to answer, especially undefined, because this involves the realization of the principle of undefined. So, after thinking carefully, write down this article, please heroes to shoot bricks. Total known: null = = undefined However: null!==

Dom is not just for JS, many other languages also implement the DOM, but Dom is already an important part of JS.BOM is a part of the JS implementation, but there is no relevant standards, so each browser has its own implementation, the problem is