JS learning notes - first acquaintance

JS The composition of

ECMAScript

ECMAScript By ECMA The international ( The former European Association of computer manufacturers ) A programming language for standardization , This language is widely used on the world wide web , It is often called JavaScript or JScript , But actually the latter two are ECMAScript Language implementation and extension .

ECMAScript: ECMAScript Specifies the JS Programming syntax and basic core knowledge , It's a set that all browser manufacturers follow JS Grammar worker Industry standards .

DOM- Document object model

Document object model ( Document ObjectModel , abbreviation DOM) , yes W3C Organization recommended standard programming interface for extensible markup language . adopt DOM The interface provided can operate various elements on the page ( size 、 Location 、 Color, etc. ).

BOM A browser object model

BOM (Browser Object Model , abbreviation BOM) The browser object model , It provides content independent 、 Object structure that can interact with browser windows . adopt BOM You can operate the browser window , Like pop-up boxes 、 Control browser jump 、 Get resolution etc .

JS Yes 3 In writing form , In line 、 Embedded and external .

Inline

<input type="button" value=" Let me try " onclick="alert ('Hello World')" />

Single or small JS The code is written in HTML In the event attribute of the tag ( With on The properties of the beginning ), Such as : onclick

Pay attention to the use of single and double quotation marks : stay HTML We recommend using double quotation marks , JS We recommend using single quotation marks

Poor readability , stay htmI Written in S A lot of code , Imitation reading ;

Quotation marks are fallible , When multiple nested quotes match , It's very easy to confuse ;

Use in special cases

Embedded JS

<script>
    alert('Hello World~!') ;
</script>

You can do more than one line JS The code writes <script> In the label

Embedded JS It's a common way of learning

external JS file

<script src="my.js"></script>

Good for HTML Page code is structured , Put a big piece of JS The code is independent of HTML Off the page , It's beautiful , Facilitate file level reuse
Quote external JS Of documents script No code can be written in the middle of the tag
Suitable for JS In the case of large amount of code

notes

 Single-line comments     ctrl + /
 Multiline comment      Default shortcut shift + alt + a

Input and output

In order to facilitate the input and output of information , JS Some input and output statements are provided in , The common sentences are as follows :