What this snippet does
Interfaces only describe shapes and contain no implementation, so they must be implemented, not extended, by classes.
Expected output
Compile Error: Classes can only extend a single class.
Why practise typing this
Typing classes code builds muscle memory for the symbols and indentation TypeScript 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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