fix(chips): use empty chip buffer if not a string

[devversion]

• Sometimes the ngModel of the custom input element (provided by the user) does not have any initial $viewValue.
• The chips component always expects the chipBuffer to be a string and a non-string reference can cause Runtime Exceptions.

Fixes #9867.

[topherfangio]

Is it ever possible for chipBuffer to be something like 3 instead of the string '3'? If so, this may fail?

[devversion]

Yeah, it could happen if the developer uses a custom input element or for example the md-autocomplete (and does have some custom ng-models)

This is kind of a safety check to ensure that there will be not Runtime errors ever.

[topherfangio]

Indeed; I'm just wondering if we could alter this to cast the input to a string instead of returning an empty string.

So, perhaps something like:

return angular.isDefined(chipBuffer) ? chipBuffer + '' : ''

This will ensure that it is always a string, or the empty string, but should handle more cases. Thoughts?

[devversion]

I thought a lot about this, and figured that just returning an empty string is the safest & cleanest approach IMO

I think casting would open more questions than it would solve, because then users might get weird chips like [Object], rather than not showing any chip.

I used the isString to avoid objects being used as truthy chip buffers.

[topherfangio]

LGTM 👍

[crisbeto]

Seems like this code was here from before, but it might be a good chance to get rid of the nested ternary expression since it's a little hard to read/follow. Also the this.userInputElement[0].value can be reduced to this.userInputElement.val().

[ppham27]

Should this JSDoc annotation be changed if this.chipBuffer is not necessarily a string?

See: https://github.com/DevVersion/material/blob/4c0c7f9cc0fa7f24a108b08d849cf905183e6451/src/components/chips/js/chipsController.js#L79

[topherfangio]

@ppham27 I think that's okay the way it is. Although you can technically force it to be something other than a string, it should always be a string.

[devversion]

@ppham27 Yeah this is fine. Also the chipBuffer variable is always a string, because it is from our internal ngModel and can't be overwritten with custom ngModel formatters by the user.