map

Transforms each value of the stream.

Signature

map(project: (value: T, index: number) => R): OperatorFunction

Marble diagram

in:    --1--2--3--|
map*10: --10-20-30-|

What it does

Applies a pure function to each next and emits the result. The project function's second parameter is the emission index (from zero), handy for numbering.

When to use

Any pure value transformation: parsing JSON, picking a field (map(r => r.data)), formatting, DTO → ViewModel. It's the first operator you reach for, and it's often enough.

See also

tap, switchMap, scan