fix(props): handle misspelled keys on prop validation object

[Alex-Sokolov]

What kind of change does this PR introduce? (check at least one)

• Bugfix

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

Other information:

When using object for validating props, there are no checks about object content. This may take a long time before noticing that you forget to pass required prop, but there are no warnings with a misprint.

Fail cases:

• Typo in key name deafult: false or require: true
• Using non-english letter in key name (for example, russian)

P.S.: Will be great to add instance sections names validation, but I have no idea how to solve this (once I spent a lot of time before see that writed component: {} section instead components: {}).

[yyx990803]

Thanks for the PR. Placing the check in assertProp incurs more runtime cost than necessary (even only in dev mode) as assertProp is also called on every re-render of the component. This check only needs to be done once in initProps.

[Alex-Sokolov]

@yyx990803 Thanks for info — moved to initProps!

[yyx990803]

Thanks for the update - as I was reviewing again I realized the runtime cost can be further reduced by placing the check here when the options are normalized... (performed once per constructor)

Also, even though this is dev-only code, I'd prefer to refactor to use a for...in loop to get rid of the iteration functions.

[Alex-Sokolov]

@yyx990803 done

[hoopyfroody]

This warns about anything which relies on adding custom attributes to the prop object. For instance this: vue-leaflet/Vue2Leaflet#109.

In another use-case, we add a note attribute to props for generating documentation.

I would suggest making this warning configurable somehow.

[JounQin]

A custom key meta like vue-router would be enough.