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Donate← JavaScript Foundations
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Lesson 14 — Group with reduce
reduce can build an object
reduce is not only for sums. Start it with an empty object {} and it can count or group things. For each word, add 1 to its counter; (acc[w] || 0) means "the current count, or 0 if this word is new".
acc["a"] = (acc["a"] || 0) + 1;
Why it matters: counting and grouping power every chart, tag cloud and report.
Want it another way?
Task
Inside reduce, add 1 to acc[w] (starting from 0), then log each word count.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
Test your knowledge
Test your knowledgeA quick 3-question quiz on this lesson — instant feedback.