javascript - check if var is in array

Question

I have two arrays of integers a=[1,3,5,7] and b=[2,4,6,8]. Now I need to check if a given var $v is in a and if it is, return the equivalent element from b. Example:

if $v in a (and $x is its position) return $b[$x].

How do I perform this?

Answer 1

the indexOf method will return the index of the array where the item was found, or -1 if it wasn't found.

var i = a.indexOf(v);
if (i != -1)
{
    return b[i]
}

EDIT: This will add the method if your browser doesn't have it.

if (!Array.prototype.indexOf)
{
    Array.prototype.indexOf = function(x)
    {
        var i;
        for (i = 0; i < this.length; i++)
        {
            if (this[i] === x)
            {
                return i;
            }
        }
        return -1;
    }
}

Answer 2

Loop through the items in the array:

for (var i = 0; i < a.length; i++) {
  if (a[i] == v) {
    return b[i];
  }
}
return -1; // not found

Answer 3

var i = a.indexOf(v);
if (i !== -1)
{
    return b[i]
}

Answer 4

if(a.indexOf(v) > -1) {
  var id = a.indexOf(v);
  console.log(b[id]);
}

See for compatibility of Array.indexOf

Answer 5

I suppose this would work.

>> function test(k){ return b[a.indexOf(k)]}

>> test(1)
2

>> test(9)
undefined

In js, indexOf always returns an integer and by calling an array with an integer (like A[3] ), it always returns a value or undefined. explicitly check for the undefined value if you want to make sure application code is not broken.

Answer 6

You may want to give below function a try. PHP.js is really a great collection of functions and salute to all contributors to make it what it is today.

http://phpjs.org/functions/in_array:432