JavaScript RegExp – p$

When it comes to working with strings in JavaScript, regular expressions play a vital role. The RegExp object is used to create regular expressions and is particularly helpful when searching, replacing, or validating strings.

In this article, we will specifically discuss the $ character, also known as the dollar sign, when used in regular expressions alongside the character p. This pattern p$ is used to match any string that ends with the letter “p.”

Using the pattern p$

To use the pattern p$, you first have to create a RegExp object. You can do this by initializing the RegExp constructor with the pattern as the first argument and any flags or modifiers as the second argument. For example, to create a regular expression that matches any string ending with “p”, you can use the following code:

const regex = /p$/;

Or, alternatively:

const regex = new RegExp("p$");

In both cases, the regex variable will be initialized to a regular expression object that matches any string ending with the letter “p”.

Example using test() method

To check if a string matches the pattern p$, we can use the test() method available on a RegExp object. The test() method returns a boolean value indicating if the pattern matches the string or not. Here’s an example:

const regex = /p$/;

console.log(regex.test("help")); // true - string ends with "p"
console.log(regex.test("gulp")); // true - string ends with "p"
console.log(regex.test("happy")); // false - string doesn't end with "p"

In this example, regex.test() will return true for both “help” and “gulp” because they both end with the letter “p”. However, it will return false for “happy” since it doesn’t end with “p”.

Example using exec() method

Another way to check if a string matches the pattern p$ is to use the exec() method. Unlike the test() method, exec() returns an array containing information about the match, including the matched string and the index of the match. Here’s an example:

const regex = /p$/;

console.log(regex.exec("help")); // ["p", index: 3, input: "help"]
console.log(regex.exec("gulp")); // ["p", index: 3, input: "gulp"]
console.log(regex.exec("happy")); // null - no match found

In this example, regex.exec() will return an array with the string “p” as the first element, followed by the index of the match and the input string. For strings that don’t match, exec() will return null.

Example combining with other pattern

You can also combine the pattern p$ with other patterns to match more specific strings. For example, to match any string that ends with “p” and has a letter “a” somewhere in the string, you can use the following regular expression:

const regex = /a.*p$/;

console.log(regex.test("grape")); // true - ends with "p" and has an "a"
console.log(regex.test("apple")); // false - doesn't end with "p"
console.log(regex.test("mop")); // false - ends with "p" but doesn't have an "a"

In this example, the regular expression /a.*p$/ matches any string that starts with an “a” and ends with “p”. The . means “any character” and the * means “zero or more of the preceding character”. This regular expression will match any string that has an “a” and ends with “p”.

Conclusion

The use of the pattern p$ in regular expressions allows you to match any string that ends with the letter “p”. You can use this pattern with the test() or exec() methods to validate or manipulate strings in JavaScript. By combining this pattern with other regular expressions, you can create more specific patterns to match even more specific strings.