Detailed explanation of JavaScript regular expressions and cascading effects

Regular expression (regular expression) is a string matching pattern, used to check whether a string contains a string of a specified pattern. Let’s share JavaScript_regular expressions and cascading effects with everyone through this article. Friends who are interested should take a look together

1. Regular expression (regular expression)

is a string matching pattern, used to check whether a string contains a string of the specified pattern.

2. Creation of regular expressions

##

var reg = /white/;
var reg = new RegExp("white","g");

3. The regular expression modifier

i Case-insensitive
m Multi-line matching

4. Regular expression symbols

[^abc] Find any characters not between square brackets.
[0-9] Find any number from 0 to 9.
[a-z] Find any character from lowercase a to lowercase z.
[A-Z] Find any character from uppercase A to uppercase Z.
[A-z] Find any character from uppercase A to lowercase z.
[adgk] Find any character within the given set.
[^adgk] Find any character outside the given set.
(red|blue|green) Find any specified option.

^ matches the beginning of a string
$ Matches the end of the string
\s Any whitespace character
\S Any non-whitespace character
\d Matches a numeric character, equivalent to [0-9]
\D Except for digits Any character, equivalent to [^0-9]
\w Matches a number, underscore, or alphabetic character, equivalent to [A-Za-z0-9_]
\W Any non-single character character, equivalent In [^a-zA-z0-9_]
. Any character except newline character

{n,} Matches the previous item n times, or multiple times
{n,m} Matches the previous item at least n times, but not more than m times
* Matches the previous item 0 times or multiple times, equivalent to {0,}
+ Match the previous item one or more times, equivalent to {1,}
? Matches the previous item 0 or 1 times, which means the previous item is optional, equivalent to {0,1}

5, properties of the RegExp object

6. Methods of RegExp object

var patt1=new RegExp("e"); document.write(patt1.exec("The best things in life are free")); 由于该字符串中存在字母 "e"，以上代码的输出将是：
e

var patt1=new RegExp("e"); document.write(patt1.test("The best things in life are free")); 由于该字符串中存在字母 "e"，以上代码的输出将是：
True

7. Analysis (email verification) var reg=/^\w+@\w+.[a -zA-Z]{2,3}(.[a-zA-Z]{2,3})?$/;

^Start of string
$End of string
\wAny character letters and numbers, underscore
+ indicates that the previous character appears {1,}, one or more times.
@ Ordinary string
\w Any string ddd@123
. Any character except newline ddd@123.
[a-zA-Z] ddd@123.c ddd @123.n
{2,3} ddd@123.com ddd@123.net ddd@123.tv
(.[a-zA-Z]{2,3})? ddd@123. com.cn ddd@123.net

Password regularity:/^[a-zA-Z0-9]{4,10}$/
Birthday regularity:/^((19\d{2})|(200\d)) -(0?[1-9]|1[0-2])-(0?[1-9]|[1-2]\d|3[0-1])$/
Email regular: /^\w+@\w+(\.[a-zA-Z]{2,3}){1,2}$/
Postal code:/^\d{6}$/
Mobile phone number ：/^1\d{10}$/

8. Methods of String object

match 找到一个或多个正则表达式的匹配
search 检索与正则表达式相匹配的值
replace 替换与正则表达式匹配的字符串
split 把字符串分割为字符串数组
9、select对象常用事件、方法和属性.

1、事件 onchange 当改变选项时调用的事件

2、方法 add() 向下拉列表中添加一个选项

示例：

 var province=document.getElementById("selProvince").value; 
  var city=document.getElementById("selCity");
  city.options.length=0; 
  switch(province){
   case "河南省":
    city.add(new Option("郑州市","郑州市"),null);
    city.add(new Option("洛阳市","洛阳市"),null);
   break;
    …… 
  }

3、属性:

options[] 返回包含下拉列表中的所有选项的一个数组
selectedIndex 设置或返回下拉列表中被选项目的索引号
length 返回下拉列表中的选项的数目

示例：

 function get(){
   var index=document.getElementById("fruit").selectedIndex;
   var len=document.getElementById("fruit").length;
   var show=document.getElementById("show");
   show.innerHTML="被选选项的索引号为："+index+"<br/>下拉列表选项数目为："+len;
  }

4、Option对象常用属性:

text：设置或返回某个选项的纯文本值
value：设置或返回被送往服务器的值

10、数组常用的属性和方法。

属性 length 设置或返回数组中元素的数目

方法：

join( ) 把数组的所有元素放入一个字符串，通过一个的分隔符进行分隔
sort( ) 对数组的元素进行排序

****读取二维数组中的元素值：

var cityList = new Array();
 cityList['河北省'] = ['邯郸市','石家庄市'];
 cityList['河南省'] = ['郑州市','洛阳市'];
 cityList['湖北省'] = ['武汉市','宜昌市'];
 for(var i in cityList){
  document.getElementById("show").innerHTML+=i+"<br/>"; 
 }
  for(var j in cityList){
  for(var k in cityList[j]){
  document.getElementById("show").innerHTML+=cityList[j][k]+"  ”;
 }
 document.getElementById("show").innerHTML+="<br/>“; }

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