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.

The ,0 denotes the start of the search. It default starts at 0, so this is redundant. — Compass
– Compass, Commented Dec 15, 2014 at 19:29
developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… - where have you looked it up? — Bergi
– Bergi, Commented Dec 15, 2014 at 19:29
I was doing some google searches but I guess the way I was searching it wasn't really the best way. Now that I look back, I sort of how I didn't find it in my searches. Thank you very much though! — JoeL
– JoeL, Commented Dec 15, 2014 at 19:42

APerson · Accepted Answer · 2014-12-15 19:29:14Z

3

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.

answered Dec 15, 2014 at 19:29

APerson

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2 Comments

Paul Over a year ago

It should be noted that there's no good reason for doing it the way it is in the code example provided, since 0 is the default.

JoeL Over a year ago

Thank you very much! I would give an upvote but I apparently need 15 rep to do that and I don't have that yet. Gave a check though! :)

Quentin · Accepted Answer · 2014-12-15 19:29:05Z

2

From mdn:

arr.indexOf(searchElement[, fromIndex = 0])

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).

answered Dec 15, 2014 at 19:29

Quentin

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Seva Arkhangelskiy · Accepted Answer · 2014-12-15 19:30:41Z

0

0 is index from where you start the search. It is 0 by default, so you don't have to pass this parameter.

answered Dec 15, 2014 at 19:30

Seva Arkhangelskiy

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