d3.scan()

d3.scan(array[, comparator])

Performs a linear scan of the specified array, returning the index of the least element according to the specified comparator. If the given array contains no comparable elements (i.e., the comparator returns NaN when comparing each element to itself), returns undefined. If comparator is not specified, it defaults to ascending. For example:

var array = [{foo: 42}, {foo: 91}];
d3.scan(array, function(a, b) { return a.foo - b.foo; }); // 0
d3.scan(array, function(a, b) { return b.foo - a.foo; }); // 1

This function is similar to min, except it allows the use of a comparator rather than an accessor and it returns the index instead of the accessed value. See also bisect.