Description

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Beginner · 8 min

Transform and filter arrays

Use arrow functions with map() and filter() to process a collection.

Transform each value

An arrow function is another way to write a function. With an expression after =>, the result is returned automatically. map() creates a new array by applying a function to every item.

const prices = [2, 4, 6];
const doubled = prices.map(price => price * 2);
console.log(doubled.join(", "));

Output

4, 8, 12

Keep matching values

filter() creates a new array containing the items whose test returns true. Neither this filter nor the earlier map changes the original numeric array.

const prices = [5, 12, 8, 20];
const affordable = prices.filter(price => price <= 10);
console.log(affordable.join(", "));

Output

5, 8

Put it into practice

  1. Predict the output of each example before running it.
  2. Complete the coding task, then try the practice questions.

Try it yourself

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Select affordable prices

Use filter() to keep prices at or below 10. Display them joined with ", ".

Practice