How do I check whether an array contains a string in TypeScript?

You can use standard JavaScript methods such as Array.prototype.includes(), Array.prototype.indexOf(), or Array.prototype.some() to check if a string array contains a particular string in TypeScript. TypeScript is a superset of JavaScript, so these methods work the same, with added type safety.

1. Using .includes()

const fruits: string[] = ["apple", "banana", "cherry"];
const hasBanana = fruits.includes("banana"); // boolean
console.log(hasBanana); // true

• includes(value) returns true if value is found, otherwise false.
• Works in modern JavaScript (ES2016+). If targeting older JS versions, you may need a polyfill.

2. Using .indexOf()

const fruits: string[] = ["apple", "banana", "cherry"];
const index = fruits.indexOf("banana"); // number
const hasBanana = index !== -1;
console.log(hasBanana); // true

• If indexOf(value) returns -1, the value is not found. Otherwise, it gives the position in the array.

3. Using .some() for Custom Checks

const fruits: string[] = ["apple", "banana", "cherry"];
const hasBanana = fruits.some(fruit => fruit === "banana");
console.log(hasBanana); // true

• .some() is handy if you want a more complex check (e.g., ignoring case, partial matching, etc.).

4. Summary

• includes("value") → direct, simple method for arrays (ES2016+).
• indexOf("value") !== -1 → older approach, still works widely.
• some(callback) → flexible if you need advanced conditions.

Also, if you want to sharpen your JavaScript knowledge (which underpins TypeScript), check out the Grokking JavaScript Fundamentals course by DesignGurus.io. It covers essential JS concepts like prototypes, closures, and async patterns—enabling you to write more efficient TypeScript code.