same solution but i use match() instead.

wao, i barely servived the critisism, but thanks for correcting my regExp mistake.

Yes, the use of assignment here is a little bit confusing.

Although it is worth noting, that it is not enough to just change += to +, because the order of operations will be different. There should be parentheses to enclose the second part. That suggests me to believe, that the += operator was used here to omit using parens.

There is also no need to assign the new value to the name variable with +=. Return it without assignment, return name + ....

mine is more clear and a bit close to you.

I'd prefer the original one. I don't even know what "identity function" means.

Manual notification.

who can explain this solution please?

nice! it's what I want to reveal. But I have Interview test time... Thank you sir. I get something from your code.

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Neat solution!

And because JavaScript isn't Java, you don't have to worry about overflow on this._progress :D

Oh, I forgot we can use getters now. I love that.

It's defined in the "preloaded" part. I don't think you can see that when training on a kata.