javascript - What does 0 mean in indexOf? - Stack Overflow

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While I am writing some JavaScript, I came across a new code "indexOf". After read another post I thought its behaviour is as shown below but it seems not true. Can someone kindly give me an explanation about "indexOf", please?

false = -1; true = 0 and more?

I have tried to change -1 to 0 and more but then nothing happens. Just to have a better understanding about jquery/indexOf.

what I have now,

$(this).closest(row)[td_word.indexOf(keyword) !== -1 ? 'show' : 'hide']();

it search for match(es) of "keyword" from "td_word", if it is not false (!== -1, thus true) display:visible;, if it is not true (false) display:hide;.

Thanks in advance.

While I am writing some JavaScript, I came across a new code "indexOf". After read another post I thought its behaviour is as shown below but it seems not true. Can someone kindly give me an explanation about "indexOf", please?

false = -1; true = 0 and more?

I have tried to change -1 to 0 and more but then nothing happens. Just to have a better understanding about jquery/indexOf.

what I have now,

$(this).closest(row)[td_word.indexOf(keyword) !== -1 ? 'show' : 'hide']();

it search for match(es) of "keyword" from "td_word", if it is not false (!== -1, thus true) display:visible;, if it is not true (false) display:hide;.

Thanks in advance.

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Share Improve this question Follow edited Dec 22, 2017 at 1:19 Maki asked Feb 27, 2015 at 0:48 MakiMaki 63744 gold badges1212 silver badges2626 bronze badges 6

• 2 So… what’s the question? Is it “why does indexOf return -1 sometimes? – Andrew Marshall Commented Feb 27, 2015 at 0:52
• 1 And of what relevance to JavaScript's indexOf is a prior question regarding C#??? – Lightness Races in Orbit Commented Feb 27, 2015 at 0:53
• 1 indexOf is not a jQuery method. – Bergi Commented Feb 27, 2015 at 0:54
• Andrew, with the way you put it. I would then ask, what numbers can indexOf return? (-1, 0, 1) only or more? – Maki Commented Feb 27, 2015 at 0:59
• Lightness Races in Orbit, may I ask if you have a link for the bloomin' documentation you mentioned? I am not sure what you are talking about on C#. I tagged jquery only before Bergi edited. – Maki Commented Feb 27, 2015 at 1:01

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1 Answer 1

Sorted by: Reset to default 10

array.indexOf(element) returns the index of the element in the array. Read the official documentation as well.

It was designed to return -1 when the element doesn't exist, because 0 would mean that the element is in the 0th index (1st element).

Examples :

var array = ['a','b','c','d','e'];

array.indexOf('a') //0
array.indexOf('c') //2
array.indexOf('f') //-1, because it doesn't exist in array

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From what I understand in your wording, I think that you think that indexOf is used to check if a certain element exists in an array. That is just a "side-effect" of indexOf but its actual usage is getting the index of an element in the array.

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