What this snippet does
Array methods contextually type their callbacks, allowing the parameter 'x' to be inferred as a number without explicit annotation.
Expected output
1
Why practise typing this
Typing contextual typing 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.
More TypeScript practice
- Contextual typing of arrow functionsContextual Typing · advanced
- Contextual typing failure with union typesContextual Typing · advanced
- Contextual typing of object methodsContextual Typing · advanced
- Declaring variables with primitive typesBasic Types · beginner
- Typing function parameters with primitivesBasic Types · beginner
- Assigning a string to a number variableBasic Types · beginner