feat(filters): add trim filter

[austinoneil]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

feature

What is the current behavior? (You can also link to an open issue here)

There is no trim filter. This feature was in response to Issue #15018.

What is the new behavior (if this is a feature change)?

There is a built-in trim filter.

Does this PR introduce a breaking change?

no

Please check if the PR fulfills these requirements

• [yes ] The commit message follows our guidelines: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#commit-message-format
• [ yes] Tests for the changes have been added (for bug fixes / features)
• [ yes] Docs have been added / updated (for bug fixes / features)

Other information:

add trim filter. Motivation: issue #15018 requests PRs.

[petebacondarwin]

@austinoneil thanks for sending this in. Trim is an easy filter to create but we don't want to add more of this sort of stuff to the core library. Instead it should be a 3rd party module that people can install if needed. See http://ngmodules.org/

[petebacondarwin]

I think that @gkalpak was not suggesting that we add it to the core but that one could make one's own trim filter to clean up his example.

[austinoneil]

For future reference, what does the "PRs plz!" tag mean?

[petebacondarwin]

@austinoneil your assumption was correct that PRs plz! suggests that we would like people to put together a PR for an issue. In this case the request, if I understand it correctly, was to fix the currency filter to do the trimming automatically. Perhaps @gkalpak and @wesleycho could clarify?

[wesleycho]

I don't think this PR is relevant to the discussion in #15018 - that discussion was specifically about the currency filter and a particular string there being trimmed due to certain locales. One can create such a filter like this in a user's app, but this type of filter shouldn't be in core.

Instead, what I suggested was that perhaps within the currency filter the relevant string be trimmed so that the issue in particular locales would not have an extra space at the end of the string.

[gkalpak]

@petebacondarwin is right. I did not suggest we created a trim filter in core. In order to adrress #15018 (in core), we need to "incorporate" some trimming into currencyFilter. That is what the PRs plz! label refers to.

Introducing a trim filter was suggested as one of the possible workarounds for people to avoid this issues until this is properly fixed in core (by fixing currencyFilter) - not as something to be introduced in core.

Sorry, for the confusion, @austinoneil 😞 (I'll try to clarify this a bit more in #15018).

[austinoneil]

yeah, I made a new pull request. where the currency string gets trimmed, rather than adding a trim filter to the core.