Notes of a high-end programming javascript basic

2010-12-01  来源:本站原创  分类:Web  人气:103 

One. JavaScript
JavaScript is a client-side scripting language, originally intended to carry out the client form data validation consists of three parts
ECMAScript javascript core, describes the syntax and basic object javascript
DOM describes the method of operation of page content
BOM describes the method of operation of the browser
ECMAScript, DOM have been standardized
BOM is not standardized, each browser has a different implementation, such as the Navigator object, Location objects, Screen object, support for cookies

Second ECMASccipt
1. Syntax
a. identifiers, variables are case-sensitive
b. the type of variable is weak, you can change at any time type of the variable
c. end of statement ";" semicolon is optional, the default behavior for the end of statement
d. single line comment / / multi-line comment / * * /
e. braces "{}" indicates a code block

2. Variables
a. line can declare multiple variables var a = '1 ', b = 2
b. variable declaration can not directly use, such as c = 3 is valid, when the interpreter will automatically see when c declare a global variable, note the global variables, and to execute this statement will be declared.

3. The basic types, reference value, and java is similar in basic types stored in the stack, put the value of the reference value of the stack is put the memory address of the object, the object stored in the heap in
ECMAScript provides basic types: undefined, null, boolean, string, number
Each type has it that the basic scope of the text alternative (literal representations)
Using the typeof operator to test object type
The return values typeof string, number, undefined, boolean, object, function
An unassigned variable is undefined such as var a; alert (a)
For the variables, two kinds of cases is undefined, one is declared without an assignment, the other is the variable does not exist there is no return value for function, for his return if the value is undefined
A derivative is undefined null null == undefined return true undefined is not assigned to a variable declared, null point is the object of this variable is null
Figures include integer, floating point, 10-band and 16 band.
Infinitely large, infinitely small is NaN
Note that NaN == NaN returns false to determine whether a variable is a number, use isNaN to judge

4. Type Conversion
a. converted to string using toString () method. For the number, you can use the toString (2,8,10,16) into the corresponding 2-band, 8 octal, 10 decimal, 16 hex said, toString () default 10 decimal
converted to number 2 b. One way parseInt ("") and parseFloat (""), the two methods only when the string parameter is passed only effective, otherwise it returns NaN
For parseInt ("") and parseFloat ("") are from the incoming character string 0 start checking if the return is not a number, if the figures have continued testing, has been detected to an illegal character character then the conversion, so
parseInt ("123a") and parseFloat ("123.4a") will return 123 and 123.4
The difference is, parseInt can specify the hex string to be converted, and parseFloat not
c. using the Boolean (arg) Number (arg) String (arg) for the corresponding conversion
Boolean (arg) non-0 number of non-empty string (length> 0) non-empty object return true; others have returned false
Number (arg) with parseInt and parseFloat different, Number detects the entire string, and then decided to use parseInt or parseFloat, Number (true) = 1 Number (false) = 0, the corresponding figure number to return, otherwise return NaN
String (arg) arg directly call the toString () method, except that, for the null, String (null) return "null", null.toString () error, undefined as

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