How to Extract a Number from a String Before a Specific Substring in JavaScript

Learn how to extract a number from a string before a specific substring in JavaScript using arrays and regular expressions (regex).
---
How to Extract a Number from a String Before a Specific Substring in JavaScript

In JavaScript, extracting a number from a string before a specific substring can be achieved through several methods including arrays and regular expressions (regex). Whether you are dealing with plain text, logging information, or more complex data patterns, JavaScript provides versatile tools to handle these tasks efficiently.

Using Regular Expressions (Regex)

Regular expressions are a powerful way to match complex patterns in strings. To extract a number before a specific substring, we can use a combination of regex patterns.

Example Code

Below is an example of how to extract a number before a substring "foo" in a string:

[[See Video to Reveal this Text or Code Snippet]]

Explanation

Regex Pattern (\d+)(?=foo):

(\d+): Matches one or more digits and captures it in a group.

(?=foo): Positive lookahead for the substring "foo" which means "foo" should follow the digits without including it in the result.

str.match(regex):

match function returns an array where the first item is the matched string and subsequent items are the captures from the regex groups.

Using Arrays and String Functions

You can also achieve the same result by leveraging JavaScript's string and array methods.

Example Code

Here’s how you can do it without using regex:

[[See Video to Reveal this Text or Code Snippet]]

Explanation

Finding Substring Position:

str.indexOf(substring) returns the index of the first occurrence of "foo".

Slicing the String:

str.slice(0, index) extracts the part of the string before "foo".

Matching Number at the End:

match(/\d+$/) finds the number at the end of the extracted part before the substring.

Both methods are effective, and the choice depends on the specific context and complexity of your task. Regular expressions offer concise solutions for pattern matching, while array and string methods provide straightforward alternatives without the need for regex knowledge.

Experiment with both methods to find which approach best suits your needs and enhances your code readability and maintainability.