2-JavaScript syntax and rules (note

JavaScript syntax and rules

First, a comment

1, single-line comments

//

2, multi-line comments

/**/

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Second, variable

1, the statement

var 变量名;	//默认值为undefined

2, the assignment

var 变量名=值;

3. Requirements

When you declare a variable in Javascript, you need to follow the following naming convention:

1. Must begin with a letter or an underscore, the middle can be numbers, or the underscore character
2. Variable names can not contain spaces and other symbols ·
3. Javascript can not use keywords as variable names, such as: function
4. Javascript strictly case-sensitive.

4, basic data types

Similar to the basic data types in java

string	String type	'' And '' are strings, JavaScript is not a single character
boolean	Boolean	Fixed value is true and false
number	Digital Type	Any number
null	air	A placeholder
undefined	Undefined type	undefined

Note: Because undefined is derived from nul, the so undefined == null

Javascript is different from java, is weakly typed language, do not use variables strictly follow the norms, so good after a variable declaration, can be assigned a value of any type.

By typeofwhich the basic data types of variables can be distinguished

or null object, is not a bug tube

5, reference data types

Reference data types are processedObjects

Create a way

var str = new String();	//和java相同
var str = new String;	//js独有
//都可以

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Third, the operator

js operators and consistent java

The following is a java js and different places

1, comparison operators

==	equal
===	Congruent (type value)
!=	not equal to
>	more than the
<	Less than
>=	greater or equal to
<=	Less than or equal

== logic, etc., only the ratio

=== congruent, and comparison of the ratio of type

Compared with the same type and valuetureOtherwise, compared withfalse

2, logical operators

&&	and
||	or
!	not

no js &

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Fourth, a regular target

1, to create a way RegExp object

var reg = new RegExp("表达式");	//基本不用
var reg = /^表达式$/;	//常用，直接量

The amount of regular direct way is the object instead of a string

Suitable for form validation

2, test method

Will check whether the regular

var reg = /^表达式$/;
var flag = reg.test("字符串");
alert(flag);

Match returns true, does not match the returns false

3, the normal way

var reg = /表达式/;

Unless all of the characters do not meet the regular, it returns false

As long as there is a character in line with regular return true

Applies to string search, replace

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Five, JS array of objects

1, characteristics

JS array can be seen in JavaArrayListset

Each member of an array type is not limited, and can store any type

Length of the array can beAutomatically modified

2, four kinds of ways to create

1、var arr = [1,2,3];	//最常用
2、var arr = new Array();	//数组长度默认为0
3、var arr = new Array(4);
//数组长度是 4, 相当于开辟了长度为 4 的空间，每个元素是 undefined。
//（仅在显示数组时进行处理，undefined 为了方便显示变成了空字符串形式，其值本质仍然是 undefined)
4、var arr = new Array(1,2);	//数组元素是1，2

3, commonly used method

W3school

join()不会对原数组产生影响
reverse()会对原数组产生影响

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Sixth, global function (global)

1, execution

eval()

Role: for scalability enhancements program

Note: You can pass only the original data type string, pass a String object no effect.

eval("var x = 10;");
alert(x);

2, encoding and decoding

URL encoding: Chinese special symbols and hexadecimal%

Role: to ensure the integrity of the data transfer.

encodeURI() Encoded URI string

decodeURI() Decoding an encoded URI

3 difference, URI and URL's

URI is a uniform resource identifier. Name identifies the resource in detail.

URL is a Uniform Resource Locator. Network location positioning resources

Resources: information can be accessed through a browser called all resources. (Pictures, text, HTML, CSS, etc.)

Details Name URI identifies resources, including the resource name.

Network location URL to locate resources. Include http: //

E.g

http: /www.huangjihao.com/ URL is

/a.html Shi URI

htp: //www.huangjihao.com/a.htmlBoth a URL, URI is

4, the string-to-digital

a、parseInt()

Parse a string and returns aInteger

b、parseFloat()

Parse a string and returns aFloat

If a character string from the literal can not be converted to digital, then the conversion from the character began to stop, only to return in front of the correct conversion values.

If the first character of the string can not be converted to digital from the literal, then stop the conversion, return NalN NaN (Not A Number, a numeric identifier to indicate not a correct number)

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Seven custom functions / custom methods

1, the function format

function 方法名(参数列表){
    函数体
}

2 Notes

No definition Javascript functions return type, a method of writing directly behind the function name;

Define parameters without using the var keyword, otherwise an error;

Java Script function body, return can not write, you can return a specific value, or simply write return

Javascript function call is finished there must be a return value, the return value is determined according to the type and, if no specific return value, the return value is undefined;

If Javascript functions with the same name, then there is no method overloading, each covering only method,Prior to the last defined function covered by the definition

Because Javascript function overloading does not exist, so only in accordance with Javascript method name to call a function, even if the real shape to participate in the function parameters do not match, it will not affect the normal call

If the parameter is not assigned, the default value undefined

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Eight custom object

1, function constructor

format

function 对象名(){
    函数体
}

//
function Person(n,a){
    this.name = n;	//定义阶段，定义属性
    this.age = a;
    
}
var p = new Person("小黄"， "20");
alert(p.age)
alert(p.name)
p.gender = "男"; //创建对象后定义属性

2, the amount of object directly

The way to create an instance of the object directly, without building function, no longer need to create a new instance of the object, can be used directly

var 对象名 = {属性名1:"属性值1", 属性名2:"属性值2"....}
//不能再去new了

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