0.12.4 • Public • Published

    DevTools Reps

    Reps is Firefox DevTools' remote object formatter. It stands for representation.


    const React = require("react");
    let { Rep, Grip } = require("devtools-modules");
    function renderRep({ object, mode }) {
      return Rep({ object, defaultRep: Grip, mode });
      Rep({ object, defaultRep: Grip, mode }),

    What is what?


    Rep is the top-level component that is capable of formatting any type.

    Supported types:

    RegExp, StyleSheet, Event, DateTime, TextNode, Attribute, Func, ArrayRep, Document, Window, ObjectWithText, ObjectWithURL, GripArray, GripMap, Grip, Undefined, Null, StringRep, Number, SymbolRep,


    Grip is a client representation of a remote JS object and is used as an input object for this rep component.

    Getting started

    You need to clone the repository, then install dependencies, for which you'll need the Yarn tool:

    git clone
    cd reps
    yarn install

    Once everything is installed, you can start the development server with:

    yarn start

    and navigate to http://localhost:8000 to access the dashboard.

    Running the demo app

    Navigating to the above address will have landed you on an empty launchpad UI:

    Image of empty launchpad

    Click on the Launch Firefox button. This should launch Firefox with a dedicated profile, listening for connections on port 6080.

    The UI should update automatically and show you at least one tab for the new Firefox instance. If it doesn't, reload the dashboard.

    Image of launchpad

    Click on any of the tabs. This should open the demo app:

    Image of demo app

    Then you can type any expression in the input field. They will be evaluated against the target tab selected in the previous steps (so if there specific objects on window on this webpage, you can check how they are represented with reps etc, ...).

    Running the tests

    Reps tests are mochitests (see documentation on MDN).

    They are run on every pull request with Circle CI. They need a mozilla-central clone to be run locally.

    a) if you don't have a mozilla-central clone available:

    • run bin/prepare-mochitest-dev, this will create a clone of mozilla-central in your repository root folder, under /firefox.
    • run yarn run copy-assets-watch, this will continuously bundle and copy reps sources to the clone of mozilla central (as well as the tests) when you modify them
    • with another command line, cd into /firefox
    • run ./mach test devtools/client/shared/components/reps

    b) if you already have a mozilla-central clone available:

    • create a configs/local.json configuration file with the following content:
      "firefox": {
        "mcPath": "/Path/to/your/mc/clone/"
    • run yarn run copy-assets-watch, this will continuously bundle and copy reps sources to the clone of mozilla central (as well as the tests) when you modify them
    • in another terminal window, cd into your mozilla-central clone
    • run ./mach test devtools/client/shared/components/reps


    The Reps project was ported to Github January 18th, 2017. You can view the history of a file after that date on github or by running this query:

    git log --before "2017-1-17" devtools/client/shared/components/reps

    Publishing to mozilla-central



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