promise chaining in JavaScript

What this snippet does

Each .then receives the previous return value — if a then throws, execution jumps to the nearest .catch.

Expected output

20

Why practise typing this

Typing promises code builds muscle memory for the symbols and indentation JavaScript uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.

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