Mastering JavaScript: Using startsWith for String Comparisons

JavaScript's startsWith() function checks if a string begins with another string. This is useful for things like data filtering data filtering, form validation or any situation where the start of a string is important. This post shows you how it works.

How to usestartsWith in JavaScript?

To use the startsWith() function, apply the following syntax:

string.startsWith(searchString, position)

• searchString is the string you're searching for.
• position is an optional integer that specifies where in the string to start the search, defaulting to 0.

Examples

Here are some examples to demonstrate startsWith() in action:

const str = "Hello, world!";

console.log(str.startsWith("Hello")); // Outputs true
console.log(str.startsWith("world", 7)); // Outputs true
console.log(str.startsWith("hello")); // Outputs false, due to case sensitivity

Case sensitivity

Since startsWith() is case-sensitive, convert both the main string and the search string to the same case (either upper or lower) for a case-insensitive comparison.

const str = "Hello, world!";
console.log(str.toLowerCase().startsWith("hello")); // Outputs true

Practical use case

Use startsWith() to filter filenames with a specific prefix or to ensure user input begins with a required character or word, enhancing data handling and validation.