Basic learning of JavaScript (i)

How JavaScript is introduced

{#1 write directly #}     <script>        alert (' Hello Yuan ')    </script>{#2 import File #}    <script Src= "Hello.js" ></script>

2.1 Variables

1 You do not declare variable types when declaring variables. All use the var keyword;

var A;

2 A row can declare multiple variables. And can be of different types.

var name= "Yuan", age=20, job= "lecturer";

3 (understand) You can declare variables without var. if you don't use Var then it is a global variable.

4 variable name, first character can only be letter, underscore, $ dollar symbol three select one, and case-sensitive, x and X are two variables

5 variables should also adhere to one of the following well-known naming conventions:

The first letter of the Camel notation is lowercase, and the next letters begin with uppercase characters. For example:var mytestvalue = 0, Mysecondvalue = "Hi" = 0, Mysecondvalue = "Hi" = 0, SMYSECONDV alue = "HI";

Attention:

    function func1 () {                var a = 123;        b=456    }    func1 ();     //     alert (a); //     alert (b); // Not recommended

1 the end of each line can be without a semicolon. No semicolon will end with a newline character as each line

a=1;b=2; a=1 b=2;------ Error A=1b=2// recommended a=1; b=2; {a=1 ; b=2;     // recommended Add tab    A=1;    b=2;}

View Code

2 Comments Support multiline comments and single-line comments./* */ /

3 using {} to encapsulate a block of code

2.3 Constants and identifiers

Constants : data values that appear directly in the program

identifiers :

1. Consists of letters, numbers, underscores (_), Dollar signs ($) that do not begin with a number
2. a name commonly used to denote functions, variables, etc.
3. For example: _ABC, $ABC, abc,abc123 is an identifier, and 1ABC is not
4. Words that represent a particular meaning in the JavaScript language are called reserved words and do not allow programs to be redefined as identifiers

Basic learning of JavaScript (i)