Underscore: _.isEmpty Behavior on numbers

The use case I ran into this was doing something like this

_.each(cow, function(v, k) {
  if (_.isEmpty(v)) {
    // do something with k because of v being empty
  }
});

So cow.a would be treated just like cow.b and cow.c. I can code around it, but thought it would be so much neater if I didn't have to (and if it didn't break the spirit or vision of underscore)

Yep, _.isEmpty is only defined for objects an arrays. You shouldn't use it on strings or numbers.

You shouldn't use it on numbers. Strings are okay:

https://github.com/documentcloud/underscore/commit/79f65b440ad5e14ff2c624a836a3eff33465be9f
https://github.com/documentcloud/underscore/blob/322a64135dc3c4a649f102e962054310c2b39c04/underscore.js#L808

So, what alternatives we have to use on numbers?

@jashkenas or @michaelficarra: any particular reason why _.isNumber is not called with in _.isEmpty? (same way _.isArray and _.isString are being used)

Any reason why it should?

Well, yes. I'm glad you asked :-)

They way I have seen most folks use _.isEmpty is pretty much to check if a value (any value) has been assigned to a particular variable. I have seen many developers run in to issues because of this.

Even the official documentation states "Returns true if object contains no values" - and a number should qualify as a value.

If there I some type of larger implication in making this change that my I just can't see, then my 2nd-best suggestion would be to please update the documentation to clearly state that it should not be used for numbers :-)

Why would you ever want to pass a number into isEmpty, instead of just checking if the number is null?

Even the official documentation states "Returns true if object contains no values"

Quite right. In JavaScript, a number is (very sadly) not an object.

I think this could be cleared up with _.isEmpty doc tweaks. What devs are looking for is _.exists.

It makes sense for _.isEmpty(a) to mean "is a an empty object?", kind of like if the statement : if obj == {} worked on values and not on references. Therefore values like numbers would return false and so would null and undefined.

an example implementation of _.isEmpty might be:

_.isEmpty = function(a) {
  return _.isEqual(a, {}) || _.isEqual(a, []) || _.isEqual(a, '');
}

@jashkenas That's probably because in some other languages "empty" determines whether variable is empty or not :) http://www.php.net/manual/en/function.empty.php

+1 to @josser - mostly because I have a PHP background :-p
But I think just clarifying it in the documentation could also be enough. I seriously see folks run into this every other week.

I ran into this today.. I was using it with _.omit

_.omit(someObject, _.isEmpty);