• startWith (soon)
  • endWith (soon)
  • concat (soon)


Compare map with filter

Animated example
How it works


accepts 1 input stream, a project function

  • When the input stream emits a value, it is given to the project function and the resulting value is emitted

returns a new stream of projected values

Published on Monday, 25 Sept. 2017
Revised on Monday, 8 Oct. 2018


❚ map and all the other reactive programming functions will never modify the input stream. Instead, they return a new stream. This principle is called immutability.

In the video example, ▬ isChecked is used as a project function. This function accepts events from checkable elements: checkboxes, radio buttons, options of a menu, toggles, etc. It returns ✔ true if the element is checked, ✘ false otherwise.

When an action is performed on the toggle (on→off or off→on), a toggle event is emitted (read a stream of toggle events).

Cédric Soulas

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Freelance Developer Advocate. Motion graphics with code. JavaScript and Elm.

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