String Starts with Substring

Introduction

In this lab, we will explore how to check if a given string starts with a substring of another string using JavaScript. We will learn how to use for...in loop and String.prototype.slice() to get each substring of a given word, and String.prototype.startsWith() to check if the current substring matches the text. By the end of this lab, you will be able to efficiently find if a string starts with a specific substring in JavaScript.

Function to Check If String Starts With Substring

To check if a given string starts with a substring of another string, follow the steps below:

• Open the Terminal/SSH and type node to start practicing coding.
• Use a for...in loop and the String.prototype.slice() method to get each substring of the given word, starting at the beginning.
• Use the String.prototype.startsWith() method to check the current substring against the text.
• If a matching substring is found, return it. Otherwise, return undefined.

Here's a JavaScript function that does this:

const startsWithSubstring = (text, word) => {
  for (let i in word) {
    const substr = word.slice(-i - 1);
    if (text.startsWith(substr)) return substr;
  }
  return undefined;
};

You can call this function as follows:

startsWithSubstring("/>Lorem ipsum dolor sit amet", "<br />"); // returns '/>'

Summary

Congratulations! You have completed the String Starts With Substring lab. You can practice more labs in LabEx to improve your skills.