To check if Object is an Array in TypeScript, you can use the “Array.isArray()” method. The isArray() method returns true if the passed value is an array and false otherwise.
function isArray(obj: any): obj is Array<any> {
return Array.isArray(obj);
}
const testObj = { key: "value" };
const testArray = [1, 2, 3];
console.log(isArray(testObj));
console.log(isArray(testArray));
Output
In the above example, the isArray() method uses a type predicate obj is Array<any> to suggest that its result can be used to refine the obj type in situations where isArray returns true. This is particularly helpful when working with TypeScript’s type-narrowing feature.
Checking if a value is an array of a specific type in TypeScript
Using Type Guards
A type guard is a runtime check that guarantees the type in a specific scope. You can use a user-defined type guard to check if a value is an array of a particular type.
function isArrayOfNumbers(value: any): value is number[] {
return Array.isArray(value) && value.every(item => typeof item === 'number');
}
const arr1: any = [1, 2, 3];
const arr2: any = [1, 'two', 3];
if (isArrayOfNumbers(arr1)) {
console.log('arr1 is an array of numbers');
} else {
console.log('arr1 is not an array of numbers');
}
if (isArrayOfNumbers(arr2)) {
console.log('arr2 is an array of numbers');
} else {
console.log('arr2 is not an array of numbers');
}
Output
Using Generics
If you want a more generic solution that can check for arrays of any type, you can use generics:
function isArrayOf<T>(value: any, typeCheck: (item: any) => item is T): value is T[] {
return Array.isArray(value) && value.every(typeCheck);
}
function isNumber(value: any): value is number {
return typeof value === 'number';
}
const arr1: any = [1, 2, 3];
const arr2: any = [1, 'two', 3];
if (isArrayOf(arr1, isNumber)) {
console.log('arr1 is an array of numbers');
} else {
console.log('arr1 is not an array of numbers');
}
if (isArrayOf(arr2, isNumber)) {
console.log('arr2 is an array of numbers');
} else {
console.log('arr2 is not an array of numbers');
}
Output
Here, the isArrayOf() function is generic and takes in a type-checking function as its second argument. This allows you to reuse the function to check for arrays of any type by providing the appropriate type-checking function.
That’s it!
Krunal Lathiya is a seasoned Computer Science expert with over eight years in the tech industry. He boasts deep knowledge in Data Science and Machine Learning. Versed in Python, JavaScript, PHP, R, and Golang. Skilled in frameworks like Angular and React and platforms such as Node.js. His expertise spans both front-end and back-end development. His proficiency in the Python language stands as a testament to his versatility and commitment to the craft.