Issue originally made by Alpha Page (alphapage)

Description

Hello,

Babylon is locked and don't provide any plugin system to interact like acorn for example. So, if you implement a new syntax, the parser throws an error because it doesn't know about the new syntax.

It would be very usefull to be able to preprocess the source via a plugin before babylon parser.

Something like this:

 export function load(source) {
    // optionally also set the sourceMap
    source.sourceMap = generatedSourceMap;
    // the modified code
    source.code = generatedCode;
    return source;
  }

I think this feature could improve Babel and hope this could help others.

Thanks in advance for your feedback.