Better error message for undefined bound property

Given the following:

<button :value.sync="missing">click</button>

results in the following error in the Chrome console:

Uncaught TypeError: Cannot read property 'length' of undefined

There is no mention:

• that a bound property is missing
• that its name is ‘missing’
• that it’s on an element <button>
• that it come from file foo.vue

An improvement would be to say:

Error: bound object 'missing' on element``<button>``can't be found in file foo.vue

[matthiasg]

its also an issue when accessing sub properties of non-existing properties.

e.g. {{options.title}} where options is not yet defined. IMHO it would be better to follow the angular way and just resolve string interpolations with errors to empty string and only log this error in non-release mode

[davidmoshal]

Similarly, this error could be more useful if it showed which component was trying to reference this element.

vue.common.js?f9a0:1019[Vue warn]: Unknown custom element: <component-a> - did you register the component correctly? For recursive components, make sure to provide the "name" option.

thanks for the awesome project!!