Question

I would like to do something like this:

var jsonFileName = aDynamicallyGeneratedJsonFileName(),
    defaultObject = {'my': 'default', 'json': 'object'};

var cachedOrRequiredObject = require(jsonFileName, defaultObject);

I would like for cachedOrRequiredObject to be given defaultObject if jsonFileName doesn’t exist, and I would like for the require cache to keep jsonFileName as a key to defaultObject even when jsonFileName doesn’t exist.

Of course this doesn’t work — in particular require errors when it can’t find the file. I could do something like:

function myRequire (file, defaultObj) {
   try {
       return require(file);
   catch () {
       return defaultObj;
   }
}

But every execution of require is going to hit the file system to try to find file when it doesn’t exist. Is there a better way for me to do this short of duplicating require’s functionality and maintaining my own cache?

Answer 1

You have to maintain your own cache for non-existent files, require has no reason to do that. A very simple object cache is enough (and is what require() uses internally):

function requireWithDefault(path, default){
    var module
    if ((module = requireCache[path]) === undefined){
        try {
            module = require(path)
        } catch(e) {
            module = requireCache[path] = default
        }
    }
    return module
}