Join is not a function

Question

I'm playing around with PEG.js

start = keyword

keyword = a:[a-z]? {return a.join("");}

Why am I getting here the error:

a.join is not a function

when I enter a valid string like abc?

Hostess

Answer 1

join() is an array-function, you cannot use it on a string: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/join

Candlelight

[a-z]? will produce either a string containing one character or a null. If you used [a-z]* you would get an array that you could call join on. However, if you used $[a-z]*, that join would be done for you automatically, yielding a string with zero or more characters in it. – Reminiscence

Answer 2

I was facing this error when I was applying join function and then returning the result in the same string array variable, we cannot do that we should save the result in some other string type variable

Launcher