The basics you must know about JavaScript

This time I will bring you the basic knowledge that JavaScript must know. What are the basic knowledge that JavaScript must know. The following is a practical case. Let’s take a look.

The most important parts of scripting language:

Data type OperatorControl statement Array Method (function)

1. Basic knowledge

Keywords:The system defines meaningful names such as background link, etc.

Identifier: Set your own name such as class aa

Variable: can be regarded as a container for storing data. The name must start with a letter and is case-sensitive. It can be assigned multiple times after definition. Pass-by-value assignment.

Define aa var aa=1, bb=2; Add a comma in the middle and a semicolon at the end

Define and assign the value var aa = 123

Use aa

Six major data types of variables:

String string number boolean Boolean object object null empty undefined undefined

Constant ：Fixed value

Scalar:Standard variable type, such as integer floating point type string type Boolean type

For example

Var 23 Replace aaa with variable

(expression) {Execute if the expression is true} else{Execute this}

When there are more than two execution options if(){ }

　　　　　　 else{} if（）{}

　　　　　　 else{}

(variable){ case "4": alert ();

break;

case "5": alert ();

break;

default: alert ( ; If the matching case is successful, the case will be executed until the end of the break. If there is no break, the next case will be entered until the break or end position is found. No case enters default.

alert() alarm window

　confirm() selection box (the return value is true or false)

4. Operator

Arithmetic operator　+　 - 　* 　　/ ++　 -- %Take the remainder 　　

　Assignment operator　 =                                                                                                                                                                                           and type)

　Logical operators

&& and || or ! Non　Ternary operation

Expression? String concatenation The strings are preceded by the addition of numbers. The strings are adjacent and converted into string addition

　　　1+1+“1”=“21” "1"+1+1="111"

Separate quotation marks "ab" becomes "a"+"b" Add the string aa inside "a"+aa+ "b"

var idVal = "asd";
var str = "<p id="+idVal+"></p>"

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website! Recommended reading:

Analysis of the front-end layout of well-known websites

Basic knowledge about front-end css

The above is the detailed content of The basics you must know about JavaScript. For more information, please follow other related articles on the PHP Chinese website!