JavaScript if variable has indexOf an item in an array

Question

I have a variable that is set dynamically on the page. I then have a list of colors in an array. I need to see if the color variable contains one of the items within the array.

Here's the code:

var colorlist = ['Silver', 'Gray', 'Black', 'Red', 'Purple', 'White'];
var col1 = "";
var color1 = 'Titanium Silver';
for (var c = 0; c < colorlist.length; c++) 
{
    if(color1.indexOf(colorlist[c]))
    {
        col1 = colorlist[c];
    }
    else
    {

    }
}

What I would expect this to return is "Silver", but it's consistently returning the last item in the array. What am I doing wrong?

If you are using a string, remember that IE<9 doesn't have indexOf you may want to use search — nicosantangelo
– nicosantangelo, Commented May 29, 2013 at 15:31
@NicoSantangelo: it doesn't have Array.indexOf, but String.indexOf is fine. — georg
– georg, Commented May 29, 2013 at 15:54
That's correct, I tried to say that you should be careful with arrays and wrote gibberish. My bad — nicosantangelo
– nicosantangelo, Commented May 29, 2013 at 16:59

Ian · Accepted Answer · 2013-05-29 15:33:42Z

3

Change your comparison to:

if(color1.indexOf(colorlist[c]) > -1)

-1 is returned when an item isn't found, yet -1 is truthy. The only falsey number is 0. So your comparison won't work as you expect.

Take a look at this fiddle, which prints the result of the indexOf and the truthyness of the value: http://jsfiddle.net/R3Xb3/

Notice how the first one returns true because "Silver" is found in the string (at a valid index). But then the rest aren't found, the index returned is -1, and the result is true.

edited May 29, 2013 at 15:33

answered May 29, 2013 at 15:28

Ian

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3 Comments

tymeJV Over a year ago

So why would OP's loop return the last element?

Ian Over a year ago

@tymeJV Because the rest of the items in the array would return -1, which is truthy. And the OP doesn't break in the loop, so it continues

cfox Over a year ago

Stupid me! How did I miss that part! That's what happens when I stare at the same code for far too long. Thanks!

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