Language features and conventions#


Volto is developed using Babel to transpile modern JavaScript to JavaScript that browsers are able to understand and execute.

Ecma International's TC39 ( is a group of JavaScript developers, implementers, academics, and more, collaborating with the community to maintain and evolve the definition of JavaScript. They stablished a process ( where the proposals are discussed, developed, and eventually approved (or dropped). The process has five stages (0 to 4) where reaching the stage 4 means the proposal is accepted and it becomes part of the JavaScript specification.

Babel enables a series of features and syntax that the developer can use in code to develop Volto on. These features are the proposals the TC39 is working on in the different stages of evolution.

Volto uses babel-razzle-preset which in turns uses @babel/preset-env which enables the use of all TC39 proposals currently in TC39's stage 4 (

Browser compatibility#

Babel preset-env uses browserlist which gives the ability to micromanage the transformations needed by the current project depending of the browser support you are currently targeting.

By doing this, it enables the bundles to be smaller, as the resulting code does not need to support old browsers (thus, transform your code to ES5 compatible code) as Babel will apply only the required transforms that your target enviroments need. For more information:

Volto project generators use this browserlist by default (you can find it in your local package.json):

  "browserslist": [
    "last 4 versions",
    "Firefox ESR",
    "not ie 11",
    "not dead"

which you can adjust depending on the environments you are targeting in your local package.json file. You can find more information about how the queries in broserlist works in:

Support to deprecated browsers#


Volto does not support deprecated browsers from its vendor (eg. IE11).

If you still need to support deprecated browsers, you should use browserslist in your project to enable the required transforms for the target deprecated environments you have to support.

However, Volto (or its dependencies) might not be compatible with old browsers anyways, and you might need to provide some other workarounds to make the build work (and the deprecated browser not crash). You can refer to this (outdated) document in order to get some hints on how to do it.