A Beginner’s Guide to JavaScript Regular Expressions for Beginners

JavaScript Regular Expression Getting Started Guide

Introduction:
Regular Expression (Regular Expression) is a powerful and flexible text matching tool that can be used Detect and manipulate strings. In JavaScript, regular expressions can be used to quickly implement operations such as string matching, replacement, and extraction. This article will introduce the basic syntax and common methods of JavaScript regular expressions in detail to beginners, and provide specific code examples.

1. Basics of regular expressions

1. Definition of regular expressions
   Regular expressions are patterns composed of characters and special symbols, used with strings Make a match. In JavaScript, regular expressions can be created using the regular expression object RegExp. For example:

   let pattern = /abc/;

   The above code creates a regular expression pattern to match "abc" in the string.

2. Basic matching rules
   Regular expressions use special characters to implement different matching modes. Common special characters include metacharacters and escape characters. Metacharacters include ^, $, ., *, , ?, |, `, [, ], (, ), {, }`etc. For example:
3. ^: matches the starting position of the string
4. $: matches the ending position of the string
5. .: Matches any character except newline characters
6. *: Matches the previous character 0 or more times
7. : Matches the previous character 1 or more times
8. ?: Matches the previous character 0 or 1 times
9. |: Matches two Any one of one or more rules
10. ``: escape characters, used to match special characters
11. Character category matching
    Character categories can be used in regular expressions to match specific type of character. Common character categories include:
12. d: matches numeric characters
13. D: matches non-numeric characters
14. w: Matches word characters (letters, numbers, underscores)
15. W: Matches non-word characters
16. s: Matches whitespace characters (spaces , tab character, newline character, etc.)

17. S: Match non-whitespace characters
    For example:

    let pattern = /w+/;
    let result = pattern.test("hello123"); // true

    Use w # for the above code ## Matches one or more word characters and returns true.

2. The use of regular expressions

1. String matching

   You can use regular expressions
   test()Method to check whether a string matches the matching rules. It returns a Boolean value indicating whether the match was successful. For example:

   let pattern = /hello/;
   let result = pattern.test("hello world"); // true

   The above code uses the regular expression

   /hello/ to detect whether the string "hello world" contains "hello".

2. String replacement

   You can use the
   replace() method of a string to replace based on a regular expression pattern. This method accepts two parameters, the first parameter is the pattern to be replaced, and the second parameter is the new string used for replacement. For example:

   let str = "hello world";
   let pattern = /hello/;
   let newStr = str.replace(pattern, "hi");
   console.log(newStr); // "hi world"

   The above code replaces "hello" in the string "hello world" with "hi" and stores the result in

   newStr.

3. Extract substrings

   You can use the
   exec() method of regular expressions to extract substrings that match the matching rules. This method returns an array containing the matched substrings and their position information. For example:

   let pattern = /d+/;
   let str = "1 apple, 2 oranges, 3 bananas";
   let result = pattern.exec(str);
   console.log(result); // ["1", index: 0, input: "1 apple, 2 oranges, 3 bananas", groups: undefined]

   The above code uses the regular expression

   /d / to extract the numeric substring in the string.

4. Global matching

   Add the
   g modifier after the regular expression to achieve global matching. For example:

   let pattern = /abc/g;
   let str = "abcabcabc";
   let result = str.match(pattern);
   console.log(result); // ["abc", "abc", "abc"]

   The above code uses the regular expression

   /abc/g to find all matches of "abc" from the string "abcabcabc".

Conclusion:

This article briefly introduces the basic syntax and common methods of JavaScript regular expressions, and provides specific code examples. Beginners can understand and learn the basic usage of regular expressions based on these examples. Regular expressions are widely used in string processing. I hope readers can flexibly use regular expressions to solve practical problems through learning.

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