null or undefined

jquery Determines whether elements exist in a slightly different way than JavaScript, because the element selected by the selector does not return null or undefined, whether or not it exists, and to use jquery to determine whether an element exists,

There are 5 simple data types in ECMAscript, also known as basic data types: Undefined, Null, Boolean, number, and string. There is also a complex data type of--object.Undefined typeWhen you declare a variable with VAR but do not initialize it, the

Note: When I was reading ES5 two days ago, I came up with a question. Today I saw this article, but I just explained it clearly and translated it.In JavaScript, there are three main ways to convert any value into a string. This article describes

The answer is: never use it. This article in turn denies five places that seem to be usable =, and explains why. There are two operators in JavaScript to determine whether two values are equal: Strict equality operator ===, must be of the same type

I. Expressions 1. The JS interpreter can calculate it to generate a value; 2. The simplest expression is the direct amount or variable name. The value of the direct amount expression is the direct amount;[Javascript]123; "I am a string" (I + 1.7; (A

It seems that I have also seen 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! = "") And so on, suddenly felt that the write is very

1 the "visible" binding　　Purpose Use　　　　The visible binding is used to trigger the associated DOM element to be hidden or visible based on the value that you pass in the binding.Example you'll see ThisMessage only when "Shouldshowmessage" holds

Chapter I. Scope1. Understanding the ScopeIntroduction to several nounsEngine: Responsible for compiling and executing the entire JavaScript program from beginning to endCompiler: Responsible for parsing and code generator and other dirty live

The string type is used to represent a sequence of characters consisting of 0 or more 16-bit Unicode characters, the string. The string can be represented by double quotation marks (") or single quotation marks ('), so the following two strings are

1. Triggering this event when the domcontentloaded Dom tree is builtLoad page loading complete triggerNative JSfunction () { //code ... .. false );d Ocument.addeventlistener (function() { //code ... false);Jquery// domcontentloaded$ (document)

What is the scope? A: In the JavaScript you don't know, the scope is a set of rules for finding variables by name. Old saying there is "no rules inadequate surrounding area", but no radius, rules and who to use? So the individual understanding

Basic data type:Strings: StringNumbers: NumberBoolean value: Boolean True/fasleSpecial data types:Empty object: nullNot defined: UndefinedComposite data type:Objects: ObjectArrays: ArrayOne, String typeThe string type is used to represent a sequence

How to judge undefined in JSThere are two special data types in JavaScript: undefined and null, the following section describes the judgment of NULL, and the following undefined. The following are incorrect usages:var exp = undefined;if (exp = =

jquery $.trim () Remove string whitespaceGrammarjQuery.trim()function is used to remove whitespace characters at both ends of a string.RoleThis function removes whitespace characters at the beginning and end of the string (until the first

Note: This article belongs to the personal summary, the knowledge point is not complete, the wrong place, also hope forgive me. (I will revise it in the future, correction)This book: the introduction of JS and the use of HTML in the skip. (Straight

Null is a JavaScript literal that represents a null value, that is, no object is rendered. He is one of the original JavaScript values. A null value is often placed on an object that is expected, but does not refer to the parameter location of any

1. Conversions when number types appear in "+" and "-"var a = " +" Span class= "Hljs-number" >3 ; // attempt to convert 3 to String var B = 4 ; console . Log (typeof a); console . log (a+b); console . log (A-B); // attempt to convert string

Array: Each item in the arrays can hold any type of data, and the size of the array is dynamically adjusted (can contain up to 4294967295 items, approximately 4.3 billion items)[1.1] Array creation:[1.1.1] Use the array constructor (you can also

Although there are many articles on the Internet, most of them are copied and pasted, Which is obscure. I hope that through this article, I can clearly improve my understanding of apply, call, and bind, the usage of these three methods is shown

with the increase of programming practice, it is very important to find out the detection of data type slowly. I think the procedure is to process the data and display the data. Therefore, the detection of data is also important for programming.