Shulou(Shulou.com)06/02 Report--

How can regular expressions be used in JavaScript? I believe that many inexperienced people are at a loss about this, so this article summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Brief introduction

In a nutshell, regular expressions are a powerful tool for pattern matching and substitution. Its functions are as follows:

Test a pattern of the string. For example, you can test an input string to see if there is a phone number pattern or a credit card number pattern in the string. This is called data validation.

Replace the text. You can use a regular expression to identify specific text in a document, and then you can delete it all or replace it with other text.

Extract a substring from the string based on pattern matching. Can be used to find specific text in text or input fields.

Basic grammar

After we have a preliminary understanding of the function and function of regular expressions, let's take a specific look at the grammatical format of regular expressions.

Regular expressions generally take the following form:

/ love/ where the part between the "/" delimiters is the pattern that will be matched in the target object. Users only need to put the content of the pattern that they want to find a match between the "/" delimiters. In order to give users more flexibility to customize pattern content, regular expressions provide special "metacharacters". Metacharacters refer to those special characters with special meaning in regular expressions, which can be used to define the occurrence pattern of their leading characters (that is, characters in front of metacharacters) in the target object.

The more commonly used metacharacters include "+", "*", and "?".

The "+" metacharacter states that its leading character must appear one or more times in a row in the target object.

The "*" metacharacter states that its leading character must appear zero or multiple times in the target object.

"?" The metacharacter states that its leading object must appear zero or once in a row in the target object.

Next, let's take a look at the specific application of regular expression metacharacters.

/ fo+/ because the above regular expression contains the "+" metacharacter, it can match the string of "fool", "fo", or "football" in the target object where one or more letters o appear successively after the letter f.

/ eg*/ because the above regular expression contains the "*" metacharacter, it can match strings such as "easy", "ego", or "egg" in the target object that have zero or more letters g after the letter e in succession.

/ Wil?/ because the above regular expression contains "?" Metacharacters that can match "Win" or "Wilson" in the target object, such as a string with zero or one letter l after the letter I.

Sometimes I don't know how many characters to match. In order to adapt to this uncertainty, regular expressions support the concept of qualifiers. These qualifiers can specify how many times a given component of a regular expression must appear to satisfy a match.

{n} n is a non-negative integer. Match the determined n times. For example,'o {2} 'does not match the' o'in 'Bob', but does match the two o in 'food'.

{n,} n is a non-negative integer. Match at least n times. For example,'o {2,} 'does not match' o'in 'Bob', but does match all o in 'foooood'. O {1,}'is equivalent to 'oasis'. O {0,}'is equivalent to 'oval'.

{n ·m} m} m and n are non-negative integers, where n

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.