Mounting compositions to the DOM

Compositions are mounted or appended to the DOM, using a "mounter" function.


A "mounter" is the main module used by the Preview Aspect to render the content of files (modules) for the 'compositions' preview. It is analogous to the docs' template. Learn more in Preview overview

Setting a mounter

To set your own template, create a new Env (or extend and existing one), and implement the getMounter() service handler.

getMounter(): string

getMounter should return the path to the file with the mounter function.

For example:

// my-react.env.ts

import { DevEnv } from '@teambit/envs';

// ...

export class MyReactEnv implements DevEnv {
  // ...

  getMounter() {
    return require.resolve('./path-to-mounter');

See the DevServer service to learn how customize the bundling of the compositions in development.

See the Bundler service to learn how to customize the bundling of compositions for previewing in distributed components.

Creating a mounter

Mounter function

The mounter fle should export, as default, a function that handles the mounting or rendering of compositions.

For example:

import React from 'react';
import ReactDOM from 'react-dom';
import { RenderingContext } from '@teambit/preview';

import { CompositionsApp } from './compositions-app';

export default (Composition: React.ComponentType, previewContext: RenderingContext) => {
    <CompositionsApp Composition={Composition} previewContext={previewContext} />,

Mounter function arguments

The Compositions Aspect invokes the mounter function and passes the following arguments:

  1. Composition: any: The composition to render. The type of Compositions varies from one Env to another (for example, compositions for React components will be of type React.ComponentType)

  2. previewContext: RenderingContext: The rendering context provides information regarding the executed aspects.

class RenderingContext {
  private contexts;
  constructor(contexts: RenderingContextSlot);
  get(aspectId: string):
    | {
        [key: string]: any;
    | undefined;

It is mainly useful (in the context of compositions) to set context providers in a React-based mounter. For example:

// Example: Wrapping the composition with context-providers

export function CompositionsApp({
}: {
  Composition?: React.ComponentType;
  previewContext: RenderingContext;
}) {
  // Get data regarding the currently running `teambit.react/react` Aspect (the React Env)
  const reactContext = previewContext.get(;
  // Get the available Context Providers, if there are any
  const providers = reactContext?.providers || [];

  return (
    <ErrorBoundary FallbackComponent={ErrorFallback} resetKeys={[Composition]}>
      // Wrap the rendered composition using the provided Context Providers
      <Composer components={providers}>
        <LoaderFallback Target={Composition} DefaultComponent={StandaloneNotFoundPage} />

Bit provides the Composer component to wrap components with multiple providers/decorators in a simple and elegant way.