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javascriptjqueryarrays
Chris
Chris

Reputation: 3174

Why / when does $.inArray return -1?

I was wondering why / when -1 is used in JavaScript or jQuery, respectively.

I'm using this snippet:

if ($.inArray('false', answers) > -1) {
  window.console.log('you Lose!');
}

Cheers,

Chris

Upvotes: 1

Views: 81

Answers (2)

Andreas Louv
Andreas Louv

Reputation: 47099

Because indexes is starting with 0. (0-index).

var arr = ['a', 'b', 'c'];

alert( arr[0] ) // a;

So when checking the index of an element in an array ($.inArray and [].indexOf) it would be wrong to return 0 if the element isn't present:

var arr = ['a', 'b', 'c'];

alert( arr.indexOf('a') ); // 0
alert( arr.indexOf('b') ); // 1
alert( arr.indexOf('c') ); // 1
alert( arr.indexOf('d') ); // -1

I would say that jQuery have a design flaw here, I would rather think that jQuery.inArray would return a boolean (true/false).

Upvotes: 2

Golo Roden
Golo Roden

Reputation: 150624

In this case, -1 is returned if the expression you are looking for is not in the array you are looking in.

While, according to its documentation, $.inArray returns the index of the element (if it was found), an index of -1 is impossible: This is due to the fact that indices start with 0 as lowest possible value.

Hence -1 does just mean a non-valid index position, i.e. not found.

So, in your snippet, the test for > -1 means: Check whether any valid index was found, or in other words, check whether the given value was in the array.

This is even mentioned in the documentation:

Because JavaScript treats 0 as loosely equal to false (i.e. 0 == false, but 0 !== false), if we're checking for the presence of value within array, we need to check if it's not equal to (or greater than) -1.

Hope this helps :-)

Upvotes: 3

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