What Is substring in js? - Scribblers Den

If you’re a JavaScript developer, you’ve probably come across the term “substring” at some point. But what exactly is a substring in JS? In this article, we’ll explore the concept of substrings, how they work in JavaScript, and some use cases for working with them.

Introduction

A substring is a subset of characters within a larger string. In other words, if you have a string like “Hello, world!”, a substring could be “world”. In JavaScript, you can extract substrings using the substring() method.

The `substring()` Method

The substring() method is a built-in JavaScript function that allows you to extract substrings from a string. It takes two arguments: the starting index and the ending index. For example, let’s say we have the following string:

const myString = "Hello, world!";

If we wanted to extract the substring “world”, we could use the following code:

const mySubstring = myString.substring(7, 12);

Here, the first argument (7) is the starting index (which is the index of the “w” in “world”), and the second argument (12) is the ending index (which is the index after the “d” in “world”). The substring() method returns the characters between these two indexes.

The Difference Between `substring()` and `substr()`

It’s worth noting that there’s a similar method in JavaScript called substr(). While both substring() and substr() allow you to extract substrings from a string, there’s one key difference: the second argument for substr() is the length of the substring, not the ending index.

For example, let’s say we have the following string:

const myString = "Hello, world!";

If we wanted to extract the substring “world” using substr(), we could use the following code:

const mySubstring = myString.substr(7, 5);

Here, the first argument (7) is the starting index (which is the index of the “w” in “world”), and the second argument (5) is the length of the substring (which is 5 characters long).

Use Cases for substring in js

Now that we understand what substrings are and how to extract them using the substring() method, let’s take a look at some use cases for working with substrings in JavaScript.

Validating User Input

One common use case for substrings is validating user input. Let’s say you have a form where users are supposed to enter their phone number. You might want to make sure that the user entered a valid phone number format (e.g. “123-456-7890”). One way to do this is by extracting substrings and checking that they match certain patterns.

For example, you could use the following code to check if a string matches the phone number pattern:

const phoneNumber = "123-456-7890";
const areaCode = phoneNumber.substring(0, 3);
const firstThreeDigits = phoneNumber.substring(4, 7);
const lastFourDigits = phoneNumber.substring(8);

if (areaCode.match(/^\d{3}$/) && firstThreeDigits.match(/^\d{3}$/) && lastFourDigits.match(/^\d{4}$/)) {
  // valid phone number format
} else {
  // invalid phone number format
}

Parsing Strings

Another use case for substrings is parsing strings. Let’s say you have a string that contains data in a certain format (e.g. “firstName lastName:[email protected]“). You might want to extract specific pieces of data from the string. You can use substrings to do this by identifying the starting and ending indexes of the data you want to extract.

For example, let’s say you have a string containing a person’s name and email address:

const fullNameAndEmail = "John Doe:[email protected]";

To extract just the name, you can use the substring() method like this:

const name = fullNameAndEmail.substring(0, fullNameAndEmail.indexOf(":"));

Here, the indexOf() method is used to find the index of the colon (which separates the name from the email address), and then the substring() method is used to extract the characters from the beginning of the string up to the colon.

Replacing Text

A third use case for substrings is replacing text within a string. Let’s say you have a string that contains a placeholder text that you want to replace with a dynamic value:

const myString = "Hello, [name]!";
const name = "John";

To replace the placeholder text with the actual name, you can use the replace() method along with substrings to extract the placeholder text:

const replacedString = myString.replace("[name]", name);

This code uses replace() to find the placeholder text (which is enclosed in square brackets) and replace it with the value of the name variable.

Conclusion

we’ve explored what substring in js are, how to extract them using the substring() method in JavaScript, and some use cases for working with substrings. By understanding substrings and how to work with them, you can add more functionality and flexibility to your JavaScript code.

Thank You

Introduction

The substring() Method

The Difference Between substring() and substr()