JavaScript The composition of :

JS characteristic :
JS It's a door Scripting language : No compilation required
compile : Translate the code into the binary language recognized by the computer .
JS It's a weak type language : Declare variables with var
JS Is a dynamic language : Knowing what kind of variable is at present
JS It is an interpretive language

JS The original purpose is to solve the problem of interaction between browser and server ( Like verifying passwords )
JS What can we do now ?
Problems of interaction 、 Special effects 、 game 、 Development of server side 、 Mobile development

HTML: Display information
Css: Beautify the page
JS: Realize the interaction between browser and server , Ability to calculate and verify
Scripting language : No compilation required , Direct operation
JS What you point out may not work , Things that can't be ordered may be ()
You need to understand .... Long term process ) object
JS What should we pay attention to :
1) Variables can be declared in case ;
2) Weak type language , Declare variables with var
3) You can use single quotation marks or double quotation marks for strings (JS Single quotation marks or double quotation marks in are strings )
* Double quotation marks are recommended ( Forced to use single quotation marks .... and DOM When you combine ( and html When nesting ))
4) Use a semicolon at the end of each line of code ;

JS The comments in :
Single-line comments ://
Multiline comment :/* Content of notes */
HTML The comments in : <!-- -->
Css Notes and JS It's the same as multiple line comments in

JS Where to write the code for :
stay script Write in Tags , It can be written in html Anywhere on the page ( Generally written in the book head At the end of the label ),script There can be multiple pairs of .

JS:1) inline , Embedded in the html in
2) Internal references , Directly on the page script Write in Tags js Code
3) External reference ,js The code is put in a js In file , Let the queen html Page .
<script src=”js Path to file ”> </script>
Be careful : You can't introduce outside JS Of documents script Write the code in the tag ( Sometimes it's wrong )
If in script There is an error in the code in the tag , It's going to affect the right script The code behind the tag executes , But it won't affect the rest of the rest script Content in Tags .

Sync : One person does many things in order
asynchronous : Many people do many things

Exchange the values of two variables 1) Third party variables 2) Use addition and subtraction
3) An operation ( Exclusive or operation )

Naming conventions for variable names :

Variable declaration can declare more than one variable at a time . Var num=10, i=10;

JS Data type of :

Generally in JS in :

Var sex=1; // male
Var sex=0; // Woman

String properties : Immutability
Tab key : Indicates alignment
Other types are converted to strings :

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