javascript concatenate variables

This article mainly introduces the scope and scope chain of Javascript variables. This article uses an instance and running result to explain these two knowledge. For more information, see the following, js learning is not very good. It's just a little idle time on the weekend. I just want to buy this "js authoritative guide" and the famous rhino book. Let's take a deep look at js. The first impression I ha

JavaScript saves and computes the writing of numeric type variables on the page, and javascript writes Previously, the following javascript snippet was embedded in the html page. However, when you click a button, the I value is added. However, after you click the button twice, the initial value of I is not changed.Cop

Analyze JavaScript variable types in detail and javascript Variables Variable type There are only 6 types: Four primitive data types: boolean, number, string, undefine, and other objects. function is an object. Typeof, instanceof View instances directly: var obj = null; console.info(typeof obj); //Object var arr = []; console.info(arr instanceof O

Analysis of the use of undefined variables or values in javascript, javascript undefined This article describes how to use undefined variables or values in javascript. We will share this with you for your reference. The details are as follows: Undefined values cannot be used

Syntax rules for declaring variable names in JavaScript, and variables declared in javascript I. Syntax Rules 1. The variable must start with a letter, underscore (_), or dollar sign ($. 2. You can then use any number of English letters, numbers, underscores (_), or dollar signs ($. 3. Javascript keywords and reser

= 1; returnBar//return 3;}varA = 0;varb =foo (a); console.log (a)//0Console.log (b)//1//if return 3 gets 3//do not add return,functionFoo2 (bar2) {bar2= 1;}vara2 = 0;varB2 =foo2 (a2); console.log (a2)//0Console.log (b2)//undefinedReturn is for returning the function value, it really has no special magical effect.In fact, directly delete the return, try to know if it is, how can I doubt this.wait, Why does the above a not be modified, is it related to a is a number?The problem here should be on t

This article mainly introduces how to write numeric variables stored and computed in JavaScript on the page. it is very useful when you need to constantly calculate a numeric variable on the page. normal writing cannot work properly, you can use this document to embed the following javascript snippet on the html page. However, when you click a button, you can add

The clever use of local variables can effectively improve javascript performance. The following is a good example. You can refer to the deeper location of an identifier in javascript, and the slower the reading and writing speed. Therefore, the fastest reading and writing of local variables in a function, and the slowe

This article mainly introduces the differences between variables with and without var in javascript definition. it uses a simple example to analyze the implementation principles and usage differences between variables with and without var in definition, if you need a variable, you can refer to the examples in this article to analyze the differences between var an

The three most basic data types in javascript: numeric, Text, Boolean.Numeric types are divided into integers and floating-point numbers.Text type is a character or string, placed in double quotation marks "" or single quotation mark "can be, if the string contains quotation marks, you can use the escape character, \ ' \", the other common escape characters: \ \ backslash, \ n line break, \ r carriage, \ t tab tab,\b backspace character, \f page break

This article mainly introduces how to define variables and variable priorities in JavaScript. Is the definition of variables so well-tuned? I believe you will have some gains after reading this article, for more information, see the following code: The Code is as follows: If (! ("Aa" in window )){Alert ('Oh my God ');Var aa = 1;}Alert ("aa" in window );Alert (

contains variables defined by "implicit", the variable at this layer will be modified without generating a new variable on the window. (This bug is also annoying, especially the encapsulated complicated code) For example: The Code is as follows: Var x = "window. x ";Function (){Var x = "a's x ";Var B = function (){Var c = function (){// No var!X = "c's x :";};Alert ("before c run, the B. x:" + x );C ();Alert ("after c run, the B. x:" + x );};Alert

This article mainly introduces examples of declaring variables or functions in JavaScript in advance. This article describes a small technique or feature. For more information, see the following example, see the following example. (You can use the Chrome browser, and then right-click F12/or review the elements. Call out the developer tool and enter the console)(TIPS: Shift + Enter in the console can be use

To check whether a variable exists, though simple but careful, the following are some points, if you encounter similar problems, you can refer to the fact that when writing JavaScript programs, you often need to check whether a variable exists. This is a very simple task, but if you are not careful, you will also encounter some problems. There are several main points: 1. Common variables The Code is as

The first more important concept about JavaScript is the variable, and the working mechanism of the variable is the basic feature of JavaScript. In fact, a variable is one of the identifiers. This article describes the variables and identifiers in more detail Defined　 An identifier (Identifier) is a name that is used to name a variable, function, property, para

The operation of a computer program needs to operate on values such as the number 3.14 or the text "Hello World", where the type of value that can be represented and manipulated is called the data type (type), and the most basic feature of a programming language is the hosting of multiple data types. When the program needs to keep the value for future use, it assigns the value to a variable (variable). A variable is a symbolic name for a value, and a reference to a value can be obtained by name.

For a programming language, you must include variables and data types. Today we'll take a look at the variables and data types of JavaScript scripting languages. RelativeIn other advanced programming languages such as java,c++, JavaScript is simple.One, variableJavaScript variables