The indexOf method in Javascript

Question

I'm trying to understand a lot of the basic components of Javascript and one of the things I came across is a line of code saying

if (varX.indexOf(String(varY),0) < 0)    

varX being an array of Strings and varY being obviously one of the strings within that array. Take away the ",0" and I understand that the code is just looking for varY withing array varX. But I don't know what the ,0 does and what means for the if statement. I did what I could to look this up and didn't really come across anything.

Answer 1

According to the MDN docs:

fromindex

The index to start the search at. If the index is greater than or equal to the array's length, -1 is returned, which means the array will not be searched. If the provided index value is a negative number, it is taken as the offset from the end of the array. Note: if the provided index is negative, the array is still searched from front to back. If the calculated index is less than 0, then the whole array will be searched. Default: 0 (Entire array is searched).

So, passing in "0" is pretty much pointless, as it starts off the search at 0 anyway.