JavaScript Intermediate Live preview

Array methods: map, filter and reduce

Transform, select and total a list of quiz scores without a single for loop.

Updated 5 Oct 2026 13 lines 1 min read

What you will learn

Create a new array with map()
Keep only some items with filter()
Combine items into one value with reduce()

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const scores = [45, 72, 88, 39, 91, 66];

// map: a new array, one result per item
const percentages = scores.map(score => score + '%');
console.log('As percentages:', percentages);

// filter: only the items that pass a test
const passed = scores.filter(score => score >= 50);
console.log('Passed (50 and above):', passed);

// reduce: combine everything into one value
const total = scores.reduce((sum, score) => sum + score, 0);
console.log('Average score:', (total / scores.length).toFixed(1));

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