JS and DOM relationship

Html browser has rendered the function code, the html source (e.g., div, p tag, etc.) to form a DOM object in memory

Document Object Model DOM (Document Object Model) standard defines the access method and process HTML documents. DOM HTML document will appear as a tree structure (a node tree) with the elements, attributes, and text.

HTML documents can be said to constitute a collection of nodes, and three common DOM node:

1. The element node: figure above <html>, <body>, <p> are all elements of the node, i.e. the label.

2. The text nodes: the content presented to the user, such as <li> the contents of JavaScript, DOM, CSS and other text.

3. attribute node: element properties, such as link attribute href <a> tag = "http://www.imooc.com".

BOM objects (the address bar of the browser, history, DOM, etc. mounted on an object)

Internal browser has JS interpreter / engine; JS html code will be executed in the engine, the result is an operation performed on the DOM object (i.e., the label is a tree within the node operation)

Add effects JS: JS operate with nothing more than just DOM objects

JS manner of introduction

JS code can be written anywhere in html, but the browser parses the code from top to bottom, note at this time whether to parse the html tag, allowing JS accessibility to the DOM object, so sometimes we put the code into html end, that is, </ html> before

Directly written in html: <script type = "text / javascript"> codes </ script>

In through the external reference: <script type = text / javascript src = ""> </ script>

To prevent slow page loads, you can put non-critical JavaScript into the bottom of the page

Declaring Variables

var variable name; variable names are case-sensitive; var statement will not pollute the global variable; the variable name with a letter, underscore, dollar sign at the beginning, later digitally

Function code segments to complete a specific function;

Common method

Output statements to html using document.write ( "")

Confire (): Message confirmation dialog; click OK to return true

Operators problem

Splicing operators: +, if the sum is a number, the connection character; As 2 + 3 + 'love' + 4 + 5 // output 5love45

PHP and different, usually with.

Logical operators or: Returns the value of true; such as:

There are a = 1;

was b = false;

var d = (a || b); // d 为 1

And logical operators: Returns the value of the variable rearmost

There are a = 22;

var b = 33;

alert (a && b); // Output 33

And operating an array of objects

JS array of key figures in increments only from 0

Note: the array brackets, JS in length; objects with braces

Use the built-in objects Js

window object

JS window object and it does not matter; the browser is an array of objects for JS to operate.

Window.open()

Scope

Case 1: This parameter is not found within a function, we will always keep looking outside, until the global space (outside the function) to find the window property

Case 2: var declare variables; declared in the local variable belongs only function within the function. If the direct assignment, without var (such as: a = 10). Would have been out looking for this variable, the assignment to find it, or else assign the default window variable name