How to Compare Strings in TypeScript

In TypeScript, as in JavaScript, strings can be compared for equality and ordering. This guide will take you through various methods and best practices for comparing strings.

Basic Equality Comparison

The simplest way to compare strings is using the === (strict equality) operator. This checks if the strings are of the same value and type.

const str1: string = "hello";
const str2: string = "hello";
const str3: string = "world";

console.log(str1 === str2); // true
console.log(str1 === str3); // false

Case-Insensitive Comparison

Sometimes, we want to compare strings in a case-insensitive manner. A common approach is to convert both strings to the same case (either upper or lower) before comparison.

const str1: string = "HELLO";
const str2: string = "hello";

console.log(str1.toLowerCase() === str2.toLowerCase()); // true

Locale-aware Comparison

For strings that may contain characters from various languages, a locale-aware comparison is essential. Use the localeCompare() method:

const germanStr1: string = "ä";
const germanStr2: string = "z";

console.log(germanStr1.localeCompare(germanStr2)); // -1 because "ä" comes before "z" in German sorting

The localeCompare() method returns:

• 0 if the strings are equal
• A negative number if the reference string comes before the compare string
• A positive number if the reference string comes after the compare string

Comparing String Lengths

To compare the lengths of strings, you can simply use the length property of the string.

const str1: string = "apple";
const str2: string = "bananas";

console.log(str1.length === str2.length); // false
console.log(str1.length > str2.length);   // false
console.log(str1.length < str2.length);   // true

Using the startsWith() and endsWith() Methods

These methods allow you to check if a string starts or ends with a specific substring.

const mainStr: string = "TypeScript is great!";

console.log(mainStr.startsWith("Type")); // true
console.log(mainStr.endsWith("!"));      // true

Handling null and undefined

If there's a possibility that your string variables might be null or undefined, it's a good practice to handle these scenarios before comparison.

const str1: string | null | undefined = getSomeString();
const str2: string = "test";

if(str1 && str1 === str2) {
  console.log("Strings are equal");
} else {
  console.log("Strings are not equal or str1 is null/undefined");
}

In this guide, we explored various methods to compare strings in TypeScript. Depending on the specific needs of your application, you can pick the method that suits best. From basic equality checks to more nuanced locale-aware comparisons, TypeScript offers flexible tools for string comparisons.