use different babel preset when running mocha tests - npm

Question

My npm package build runs with babel and I configured a babel preset in my package.json with
"babel": { "presets": ["es2015"] }
I also configured a mocha test script with
"test": "mocha --compilers js:babel-core/register"
However, I would like to run my tests using a different babel preset than that one specified for my build.
Is it possible? I would you achieve that?

Answer 1

Babel accommodates environment variables so you could set a test environment variable and alter your presets accordingly:
In your package.json:
"babel": {
"env": {
"test": {
"presets": [/* your test presets */]
}
},
"presets": [/* your usual presets */]
}
Then, run your mocha command like so:
"test: BABEL_ENV=test mocha --compilers js:babel-core/register"

Answer 2

You could create a file named babel-hook.js and put in it:
require("babel-register")({
presets: [ /* whatever values you want here */ ],
});
then run Mocha like this:
mocha --require babel-hook
This will register Babel and you can use any configuration option you want with it, separate from anything in package.json.

Answer 3

The answer about configuring babel in package.json was partially ok.
I needed to add seperate env entries to make it work cause otherwise the config outside env would always run.
So the final configuration example would look like this:
"babel": {
"env": {
"test-console": {
"presets": ["#babel/preset-env"],
"plugins": ["#babel/plugin-proposal-class-properties"]
}
,
"test": {
"presets": ["#babel/preset-env"],
"plugins": ["#babel/plugin-proposal-class-properties", "transform-remove-console"]
}
}
And scripts:
"scripts": {
"test-console-log": "BABEL_ENV=test-console mocha || TRUE",
"test": "BABEL_ENV=test mocha || TRUE"
}