Shouldn't the prop check for a default value first? It would keep it more in line with what happens if you omit the prop completely.

Here's another JSBin showing the different ways to pass a non value prop through. I'm thinking it should fall back to the default value in all cases.

I have thought about this before, and didn't implement it because user may explicitly want to pass down undefined - but now I think it is appropriate to map it to the semantics of JS function calls so that default value would be used if the passed down prop is undefined.

See 04116fc

Thanks. I was going to suggest a nullable prop option for allowing nulls to be passed down in the case of none required props. In this case, the default would only apply if the prop was completely absent.

@yyx990803 I'm a bit confused by the commit, it says

`if (raw === null) {
// initialize absent prop

•    initProp(vm, prop, getDefault(vm, options))
  

•    initProp(vm, prop, undefined)`
  

but I can't see any code for handling undefined, and the commit actually says that if it is null, then it's set to default.

when is undefined passed as a prop handled?

// check default value
if (value === undefined) {
value = getPropDefaultValue(vm, prop, key);
// since the default value is a fresh copy,
// make sure to observe it.
var prevShouldConvert = observerState.shouldConvert;
observerState.shouldConvert = true;
observe(value);
observerState.shouldConvert = prevShouldConvert;
}
{
assertProp(prop, key, value, vm, absent);
}

I found this bit in vue.js v2 dist, is it around this part that defaults are now handled?

I can't find a comment of

Build a function that applies props to a vm.

anywhere in the current v2 vue.js build