ifError should throw its argument

[Magomogo]

Why ifError(arg) doesn't throw its argument as node.js' included assert module do?

[keithamus]

Hi @Magomogo thanks for the issue.

As far as I know, Assert.ifError works exactly the same way as Node.js' Assert.ifError: It throws on truthy values.

assert.ifError(false);
assert.ifError(null);
assert.ifError(undefined);

err(function () {
  assert.ifError('foo');
 }, "expected \'foo\' to be falsy");

If in doubt though, read the source. Here is Node.js' source for ifError, while here is chai's. Chai's is a little more complex, so it can interface with the standard assertion errors. Here's the ok assertion which as you can see just passes in the object as the assertion, and finally here is the underlying coercion logic. Ultimately it all resolves to be the exact behaviour that Node's assert.isError exhibits.

Do you have a specific code example that isn't working?

[Magomogo]

Hi, @keithamus!

Thanks for answering.
Just take a look on this sample:

var assert = require('chai').assert,
    error = new Error('Ouch!');

assert.ifError(error);

It gives AssertionError: expected [Error: Ouch!] to be falsy instead of an exception with stack trace.

[keithamus]

Ah. I should perhaps take some of my own advice and read the source! It does indeed behave differently. It seems like our version of ifError will throw an AssertionError if the given argument is not falsey, while node will throw the given argument.

I can't really tell you why this is different - but I can say that it is unlikely going to change any time soon; we don't have metrics on how many users use this feature, but cannot reasonably change the behaviour without potentially breaking existing users' code.

@Magomogo, if you're looking for the same behaviour as Node's assert.ifError - it should be trivial to simply inline it (if (error) throw error;). As I say, it is unfortunate that the two methods share the same name but not the same behaviour, but we're kind of stuck with our implementation for the sake of compatibility.

[Magomogo]

I understand your concerns. However it's bad that one can't just replace standard assert library with yours. Maybe makes sense to fix this behavior in major versions.
Thanks and good luck!

[lexi-sh]

Hey @keithamus , should there be a new 3.0 branch that I pull request to if I make this change?

[keithamus]

@cjqed I've just created a 3.x.x branch for you - if you make a PR to that, that will be great 😄

[lexi-sh]

So, I tried to look up things about ifError, like how it came to be and the documentation surrounding it, but:

1. The comments in the code don't say anything:

  /*!
   * Undocumented / untested
   */

  assert.ifError = function (val) {

1. And then the only thing I can find is this PR: New assertion: isError #145

I'm not really sure what the expected behavior in 3.0 should be. Should we just mimic node behavior?

  assert.ifError = function (val) {
    if (val) {
      throw(val);
    }
  };

[keithamus]

Absolutely, just mimic the Node API 100%. If it helps, tests for Node's assert.ifError can be found here and here

[toymachiner62]

What is the expect equiavlent of assert.ifError?