How to filter an Array based on a condition in Typescript?

Filtering an array based on a condition in TypeScript is straightforward and similar to how you would do it in JavaScript. TypeScript adds type safety to the process, ensuring that your code is more robust and less error-prone.

Here’s a step-by-step guide on how to filter an array in TypeScript:

Basic Filtering Example

Suppose you have an array of numbers and you want to filter out all numbers that are greater than or equal to 50.

1. Define the Array

First, create an array of numbers:

const numbers: number[] = [10, 60, 40, 90];

2. Filter the Array

Use the filter method to create a new array containing only the elements that meet your condition. In this case, you want numbers that are greater than or equal to 50:

const filteredNumbers: number[] = numbers.filter(num => num >= 50);

3. Log the Result

You can then log or use the filtered array as needed:

console.log(filteredNumbers); // Output: [60, 90]

Filtering with Objects

If you have an array of objects and you want to filter based on a property, the approach is similar.

Example: Filtering Objects

Suppose you have an array of objects representing users, and you want to filter users who are above 18 years old.

interface User {
  name: string;
  age: number;
}

const users: User[] = [
  { name: 'Alice', age: 22 },
  { name: 'Bob', age: 17 },
  { name: 'Charlie', age: 30 },
];

const adults: User[] = users.filter(user => user.age > 18);

console.log(adults);
// Output: [ { name: 'Alice', age: 22 }, { name: 'Charlie', age: 30 } ]

Using Generics for More Flexibility

If you want a more flexible solution where you can specify the type of array elements, you can use TypeScript generics:

function filterArray<T>(array: T[], predicate: (item: T) => boolean): T[] {
  return array.filter(predicate);
}

// Example usage with numbers
const numbers: number[] = [10, 60, 40, 90];
const filteredNumbers = filterArray(numbers, num => num >= 50);
console.log(filteredNumbers); // Output: [60, 90]

// Example usage with objects
const users: User[] = [
  { name: 'Alice', age: 22 },
  { name: 'Bob', age: 17 },
  { name: 'Charlie', age: 30 },
];

const adults = filterArray(users, user => user.age > 18);
console.log(adults); // Output: [ { name: 'Alice', age: 22 }, { name: 'Charlie', age: 30 } ]

Summary

• Basic Filtering: Use the filter method with a condition.
• Filtering Objects: Apply the filter method with a predicate that checks object properties.
• Generics: For reusable filtering functions, use TypeScript generics to handle different types of arrays.

These techniques ensure that your filtering operations are type-safe and easy to manage in TypeScript.