Cookbooks
TypeScript
Chapter 2. Strings
Finding the length of a string

TypeScript:
Finding the length of a string

How to:

In TypeScript, you get a string’s length using the .length property. Here’s a quick example:

let greeting: string = "Hello, TypeScript!";
console.log(greeting.length); // Output: 18

This code declares a string variable named greeting and then logs its length to the console.

Deep Dive

The .length property is a holdover from JavaScript, TypeScript’s ancestor. It’s a straightforward and universally supported way to get a string’s size.

There are alternatives, but they usually complicate things. For example, you could convert the string to an array and count the elements:

let greetingArray: string[] = Array.from(greeting);
console.log(greetingArray.length); // Output: 18

But why go the long way round? The .length property is efficient because strings are stored as character arrays under the hood, so the length information is readily available.

Now, let’s say you’re dealing with strings from different languages. You could run into issues with special characters. The basic .length approach counts UTF-16 code units, which can be problematic for characters that require two code units, known as surrogate pairs. In such cases, the .length property might not give you the count of actual characters, also known as code points.

Here’s how you can handle strings with surrogate pairs:

function countCodePoints(str: string): number {
    return Array.from(str).length;
}

let fancyGreeting: string = "Hello, 🌍!";
console.log(countCodePoints(fancyGreeting)); // Output: 9

This function deals with the intricacies of string encoding to ensure each character, regardless of whether it’s a single or double code unit, is counted properly.

See Also

Extracting substringsInterpolating a string