null or undefined

How js judges null Summary of js's method for determining null. The following are incorrect methods: Var exp = null;If (exp = null ){Alert ("is null ");} When exp is undefined, it will also get the same result as null, although null and undefined

1.$.trim (str)Remove the spaces, page breaks, tabs, line breaks, carriage returns, and other special characters before and after the passed-in string.The value of the original string STR does not change and returns the new value after the change.2.$.

http://www.cnblogs.com/446557021/archive/2011/10/13/2211043.html JS Data type conversion method mainly has three kinds ofConversion function, coercion type conversion, using JS variable weak type conversion.1. Conversion function:JS provides two

"2" Array typeEach item of the ECMAScript array can hold any type of data, and the size can be dynamically adjusted, which can automatically grow as the data is added to accommodate the new data.(1) Creating an array1 "Using the array constructorvar

Describe:Copy an object or an array (well, everything is an object, and an array is an object).If destination is omitted, a new object or array will be created;If destination is provided, all elements and attributes in the source object are copied

The two methods use the same code, one for the jquery object or for the common object, and one for the jquery object instance, and for the basic usage, give a few examples:The HTML code is as follows:DOCTYPE HTML>HTML> Head> title>title>

First, the data type1. Basic type:Number can use the isNaN function to detect if a parameter is "not a value",When you need to display special characters in a string code, use a backslash (\) to escape,Boolean any non-empty string can be converted

After parsing the string, there is not much left.5. Parameter selector is a functionThis is very easy to think of, first of all to say DOM loading. We usually have to wait for the document to be loaded when we write the script in the head, JS is so

● Constants and global functions ● Note: If the = sign is added before the function name, the function returns a value. 1. constants:True logical truth.False logical false.Null value, which can be equal to the undefined value (but of different

Document directory 1. typeof 2. Constructor 3. Object. Prototype. tostring. Call () Summary I recently reviewed John resig's masterpiece "Pro JavaScript techniques" and talked about how to judge the Javascript type. This article introduces

Preface All the code in this article is from jquery.1.5.2. For ease of understanding, the concept of class is introduced, although jquery is not based on object-oriented thinking. Jquery is now the most popular JavaScript framework. $ is the most

There are three main methods to convert JS Data Types Conversion functions, forced type conversion, and weak type conversion using JS variables. 1. conversion functions: JS provides two conversion functions: parseint () and parsefloat. The former

NounEngine: Responsible for compiling and executing the entire JavaScript program from beginning to end.Compiler: Responsible for parsing and code generation .Scope: Collects and maintains a series of queries consisting of all declared identifiers (

This article describes how to parse the deconstruct assignment in the JavaScript ES6 version. The ES6 version has brought many simplified improvements to JS. If you need it, What Is deconstruct assignment? Deconstruct value assignment allows you to

Parse the emptyis_null and isset tests in PHP. The code is as follows :? Php $ a; $ bfalse; $ c; $ d0; $ enull; $ farray (); first, the var_dump output of empty: booleantruebooleantruebooleantruebool: The code is as follows: $;$ B = false;$ C = '

Strictmode is a technology introduced by JavaScript1.8.5, but there is no reliable implementation of strict mode in the browser, so be careful when using it and perform multiple tests. Strictmode can be applied to the entire script or a single

This article does not provide a detailed description of all js operators, but lists the unique characteristics of js operators that are different from other common languages, at least it will not make us confused when reading some open-source

The map method calls the callback function once in order for each element in the original array. The returned values after each callback operation are combined to form a new array. The callback function is called only on indexes with values. indexes

---restore content starts---map()method returns a new array that consists of the return value of each element in the original array that is called after a specified method.Array.map (callback[, Thisarg])Note: [] the contents of [] within the syntax

Window. onload = function (){ 2 /**//*  3. Each object instance has an attribute member pointing to its prototype of the instanceof object (temporarily called the parent object)  4. We call this layer-by-layer relationship pointing to the parent