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promise-breaker v4.0.0 Release Notes

    • ➕ Add call() and apply().

    • 💥 Breaking Change - Previously, when using pb.callFn() or pb.applyFn(), if the called function returned a thenable, we would assume the function was Promise based, and would otherwise assume it was callback based. This leads to a dangerous problem if you call a function that returns a scalar, though:

      let fn = (str) => "hello " + str;
pb.callFn(fn, 1, null, "world")
.then(result => expect(result).to.equal("hello world"));

    Here, fn.length is 1, and we're telling callFn we want to call an async function that takes 1 parameter, not including the callback. If fn doesn't return a Promise here, the expected behavior would be to wrap the return value in a Promise and return it. In v3.0.0, we would have assumed that since fn did not return a Promise, it must be callback based, so we would wait for the callback forever. This is dangerous behavior.

    In v4.0.0, we now decide whether to treat fn as a Promise function or a callback function based on fn.length. If you call callFn or applyFn, and tell it you are expecting a function that takes 1 parameter, promise-breaker will now throw an error if fn does not take 1 or 2 parameters.