default value for Boolean is NOT undefined, it is false, which is inconsistent with other types

[tomwang1013]

Version

2.2.6

Reproduction link

https://jsfiddle.net/15ku6ck7/1/

Steps to reproduce

Just run the jsfiddle, it will output: "b is not undefined, it is: false; s is undefined"
b is of Boolean type, s is of String type

What is expected?

b is also undefined if not provided

What is actually happening?

b is false

[yyx990803]

This is a feature, not a bug. I can't think of a case where undefined is more useful - and changing it would be a breaking change for little gain.

[tomwang1013]

@yyx990803 Sometimes i want to know whether a prop is provided by parent component, so i check if it is undefined

[liuqiang1357]

@yyx990803 +1