The Concept and Application of Regular Expressions in JavaScript_Regular Expressions

This article mainly introduces the concept of regular expression in JavaScript and the related information of JavaScript application. Friends who need it For reference, the regular expressions in JavaScript will be of great help to our future development.

Today I would like to share with you some knowledge about regular expressions and their application in JavaScript. Regular expressions are simple but not simple. For example, when my teacher used to teach us, he said that if you get started with this thing, you can master it in 20 to 30 minutes. Once you don't get started, you won't be able to catch up in a few days. So I studied and researched it very seriously at the beginning. Unexpectedly, regular expressions not only simplify the code, but also save front-end engineers a lot of trouble in actual operations. As we all know, when users browse the page, the only thing that interacts with data is the form. Regarding form verification, there are actually many methods. Next, I will share with you two methods. One is an ordinary and cumbersome method. , one is regular expression, let’s see what effect it can bring to the form.

First let’s take a look at the regular version:

Personally, I feel that the method is too crude. This is what I did when I first started learning. Simple form effect without adding CSS style sheet.

Let’s take another look at the upgraded regular expression:

Continue Let’s learn about regular expressions together.

Regular expression is an object that describes a character pattern, also known as regular representation and conventional representation.

Regular expression uses a single string to describe and match a series of A string that conforms to a certain syntax rule. In many text editors, regular expressions are often used to retrieve and replace text that matches a certain pattern.

The characteristics of regular expressions are: 1. Very flexible, logical and functional; 2. Complex control of strings can be achieved quickly and in an extremely simple way. 3. It is relatively obscure and difficult to understand for those who are new to it.

Define regular expression 1: Ordinary method varreg=/expression/additional parameters

 reg.test(v.value)

2: Constructor Method

  
var reg=new RegExp("表达式","附加参数） var reg=new RegExp("china");

Expression Mode 1:

简单模式 var reg=/china/;

Expression mode 2:

符合模式 var reg=/^\w+$/; var reg=/^\w+@\w+.[a-zA-Z]{2,3}(.[a-zA-Z]{2,3})?$/;

RegExp object’s method exec retrieves characters that match the regular expression and returns the found value. And determine its position test retrieves the value specified in the string, returns true or false exec method: if no match is found, the return value is null; if a match is found, a result array is returned, /.../ represents the beginning of a pattern and end ^ matches the beginning of the 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 Any character except a digit, Equivalent to [^0-9] \wmatches a number, underscore, or alphabetic character, equivalent to [A-Za-z0-9_] \WAny non-single-word character, equivalent to [^a-zA-z0- 9_].Any character except newline character

{n} matches the previous item n times {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 or more times, equivalent to {0,} + Matches the previous item 1 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}

x|y matches x or y.

For example, "z|food" can match "z" or "food". "(z|f)ood" matches "zood" or "food". [xyz] character set. Matches any one of the characters contained. For example, "[abc]" would match the "a" in "plain". [a-z] Character range. Matches any character within the specified range. For example, "[a-z]" matches any lowercase alphabetic character in the range "a" through "z". Note: Only when the hyphen is inside the character group and appears between two characters, it can represent the range of characters; if it appears at the beginning of the character group, it can only represent the hyphen itself. (pattern) Match pattern and get this One match. The obtained matches can be obtained from the generated Matches collection, using the SubMatches collection in VBScript and the $0...$9 attributes in JScript. To match parentheses characters, use "\(" or "\)".

The above is the concept and application of regular expressions in JavaScript_all the contents of regular expressions. I hope it will be helpful to friends in need!

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