Better errors for function parameters

[rwest202]

What is wrong?

Utility functions should notify you when you make some basic mistakes, like forgetting to pass in a required parameter.

Where does it happen?

likely is one of the functions. It may be happening in more.

How do we replicate the issue?

brain.likely(input)
This will give you an error like so,

var output = net.run(input);
                 ^
TypeError: Cannot read property 'run' of undefined

However, it should give you an error like, `Required parameter 'net' is undefined'

How important is this (1-5)?

3. All considered it's not too difficult to look at the stack trace. But it's important for usability in a library.

Expected behavior (i.e. solution)

Errors that look like this, `Required parameter 'net' is undefined'

Other Comments

[robertleeplummerjr]

I really think this is a good suggestion. If you don't mind, I'd like to reopen.

[mbflex]

I am afraid that the TypeError message comes from the underlaying Java Script framework and can't be changed by the developers of the brain.js library, obviously.

Please note also, that the variable net in net.run(input) is not a "function parameter" but the object which provides the method.

[rwest202]

Yes, but you can catch the error before it happens. For example in src/likely.js you could add an if statement like so.

/**
 *
 * @param {*} input
 * @param {brain.NeuralNetwork} net
 * @returns {*}
 */
export default function likely(input, net) {
  if (!net) {
    throw new TypeError(`Required parameter 'net' is of type ${typeof net}. Must be of type 'brain.NeuralNetwork'`)
  }
  let output = net.run(input);

  // rest of code
}

[mubaidr]

implemented in: #540