Smallest number in array and its position

Just loop through the array and look for the lowest number:

var index = 0;
var value = temp[0];
for (var i = 1; i < temp.length; i++) {
  if (temp[i] < value) {
    value = temp[i];
    index = i;
  }
}

Now value contains the lowest value, and index contains the lowest index where there is such a value in the array.

One-liner:

alist=[5,6,3,8,2]

idx=alist.indexOf(Math.min.apply(null,alist))

You want to use indexOf

http://www.w3schools.com/jsref/jsref_indexof_array.asp

Using the code that you had before, from the other question:

temp = new Array();
temp[0] = 43;
temp[1] = 3;
temp[2] = 23;

Array.min = function( array ){
    return Math.min.apply( Math, array );
};

var value = temp.min;
var key = temp.indexOf(value);

Find the smallest value using Math.min and the spread operator:

var minimumValue = Math.min(...temp);

Then find the index using indexOf:

var minimumValueIndex = temp.indexOf(minimumValue);

I personally prefer the spread operator over apply.