Checking if a field with a default value has been set

[deepakmerugu]

I'm trying to figure out if an optional field has been set in a proto. Can you please explain how to check if a field has been set. Currently, I'm observing that if a field has a default value and is not set, then on decoding, the object contains the default value. How can we distinguish this from the case where the field was indeed set with the same value as the default?

Thanks!

[dcodeIO]

Currently there is no way to determine if the values have been explicitly set with the default value. There is, however, the possibility to check if the value equals the default value:

var myMessage = MyMessage.decode(...);
if (myMessage.someField === myMessage.$type.getChild("someField").defaultValue) {
    ...
}

[seishun]

The official C++ and Java implementations provide has_* methods for this functionality. But JavaScript can do better than that. Here's an API that I think would be idiomatic for JavaScript:

Consider a Message object obj and a field "foo".

• obj.foo evaluates to the value of "foo" if it's set, otherwise to the default value for "foo". If "foo" doesn't have an explicit default, then it evaluates to the type-specific default.
• obj.hasOwnProperty("foo") is true if "foo" is set, otherwise false.
• delete obj.foo clears "foo". Afterwards, obj.hasOwnProperty("foo") is false and obj.foo is the default value.

This API could be implemented by using inheritance. I can produce a proof-of-concept if anyone is interested.

[dcodeIO]

Closing this for now.

protobuf.js 6.0.0

Feel free to send a pull request if this is still a requirement.