JavaScript Note One

Javascript:

ECMAscript: Equivalent to translating computer to code interpreter

DOM Document Object Model---Documents get the entry of an element operation HTML page

BOM Browser Object Model Explorer window window Popup

Compatibility
ECMA has virtually no compatibility issues
DOM has some operations that are incompatible
BOM does not have compatibility issues (completely incompatible)
　
Variable
typeof a test data type

Number numeric type

string literal type

Boolean Burgen, False

function type

Document Object Type

Undefined:1. undefined
2. Define a value that is not given

Forcing type conversions

Parseint converting a string into a numeric coercion type convert an integer

A left-to-right scan string encounters a non-numeric immediate jump

{

Nan:not a number

parseint ("abc") =nan

Determine whether two Nan is equal:

cannot be used directly (Nan==nan)

Using function IsNaN

}

Parsefloat Convert to Decimal

Display Type conversions: parseint,parsefloat

Implicit type conversion: = = First conversion type and then comparison

Example: Var a=5;b= ' 5 '; alert (a==b)---->turn

var a= ' n '; var b= ' 5 '; alert (a+b);//1. String concatenation (direct stitching) 2. Number addition (forced type conversion)

Alert (A-B); Subtraction of numbers

Scope

Local variables and global variables

Closed Package

A child function uses a local variable of the parent function

Image matching:

Element.src.match (* * *)

Not math, but the match () method retrieves the specified value within a string, or finds a match for one or more regular expressions.

If document.write is executed after the document has finished loading, the entire HTML page will be overwritten:

Characteristics

JavaScript has a dynamic type. This means that the same variables can be used as different types to represent variable strings when both single and double quotation marks are available:

JavaScript has only one numeric type. Numbers can be with decimal points or without:

Object

The JavaScript object declares and represents the calling method. var square={height:50,width:80,name: "Yalis"};

Call: document.write (square.height);
document.write (square["height"])

Statement
var carname=new String;
var x= new number;
var y= new Boolean;
var cars= new Array;
var person= new Object;

Objects like struct types can access the properties and methods of an object (for...in)
Return statement application: You can exit a certain condition can be directly executed return;
difference between double equals and three equals sign
"=" Assignment
"= =" equals: Used for comparison, the judgment value is equal "= = =" All equals: For comparison, judging type and value

JavaScript Note One