This content originally appeared on DEV Community and was authored by Rishikesh Janrao
JavaScript ECMAScript 3 (ES3), released in 1999, was a pivotal version in the evolution of the language. One of its powerful features was the introduction of Regular Expressions (regex), which provided developers with a robust tool for pattern matching and text manipulation.
What are Regular Expressions? 
Regular expressions are sequences of characters that form search patterns. They can be used for a variety of text processing tasks, like searching, matching, and replacing content within strings.
Basic Syntax of Regular Expressions
In ES3, regular expressions are enclosed between forward slashes (/). Here are some fundamental concepts:
-
Literals: Characters that match themselves. For example,
/a/matches the character “a”. -
Metacharacters: Special characters that have specific meanings. Examples include
.(matches any character except a newline),*(matches the preceding element zero or more times), and\d(matches any digit).
Here’s a simple regex to match any digit:
const regex = /\d/;
Using Regular Expressions in JavaScript 
In ES3, regular expressions can be used with various string methods like search and replace. Let’s explore these with some examples.
Searching with search() 
The search() method searches a string for a specified value and returns the position of the match. If the value is not found, it returns -1.
Example:
const text = "Hello, world!";
const regex = /world/;
const position = text.search(regex);
console.log(position); // Output: 7
In this example, search() finds the word “world” at position 7 in the string “Hello, world!”.
Replacing with replace() 
The replace() method searches for a pattern in a string and replaces it with a specified replacement.
Example:
const text = "I love cats!";
const regex = /cats/;
const newText = text.replace(regex, "dogs");
console.log(newText); // Output: I love dogs!
Here, replace() finds “cats” in the string and replaces it with “dogs”.
Practical Use Cases 
Regular expressions in ES3 enable developers to perform various practical tasks in JavaScript, especially when combined with string methods.
Validating Input 
One common use case is validating user input. For instance, you can use regex to check if an email address is in the correct format.
Example:
const email = "example@example.com";
const regex = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6}$/;
const isValid = regex.test(email);
console.log(isValid); // Output: true
This regex checks for a basic email format and returns true if the input matches.
Extracting Information 
Regular expressions can also be used to extract specific information from a string. For example, extracting all numbers from a text.
Example:
const text = "My phone number is 123-456-7890.";
const regex = /\d+/g;
const matches = text.match(regex);
console.log(matches); // Output: ["123", "456", "7890"]
The regex \d+ matches sequences of digits, and the g flag ensures it finds all matches in the string.
Splitting Strings 
Another use case is splitting strings based on a pattern. For instance, splitting a sentence into words.
Example:
const text = "Split, this string! into parts.";
const regex = /[\s,!.]+/;
const words = text.split(regex);
console.log(words); // Output: ["Split", "this", "string", "into", "parts"]
The regex [\s,!.]+ matches spaces, commas, exclamation marks, and periods, allowing you to split the string into individual words.
Combining Regex with Other JavaScript Features 
In ES3, regular expressions can be combined with other JavaScript features to perform complex tasks.
Searching and Replacing with Functions 
You can use a function in the replace() method to dynamically generate the replacement text.
Example:
const text = "I have 2 apples and 3 oranges.";
const regex = /\d+/g;
const newText = text.replace(regex, (match) => parseInt(match) * 2);
console.log(newText); // Output: I have 4 apples and 6 oranges.
In this example, each number in the string is replaced with its double.
Conclusion 
Regular expressions in JavaScript ES3 offer a powerful way to work with text. They enable searching, matching, and replacing patterns within strings. Whether you’re validating input, extracting information, or manipulating strings, regex provides a versatile toolset that enhances your JavaScript programming.
So, dive into the world of regular expressions and discover how they can simplify your text processing tasks! 
This content originally appeared on DEV Community and was authored by Rishikesh Janrao