I am trying to create the following data structure in javascript:

d = {foo: [3, 77, 100], bar: [10], baz: [99], biff: [10]}

My starting data structure is a a list of dictionaries:

input = [{key: foo, val: 3}, {key: bar, val: 10}, {key: foo, val: 100}, {key: baz, val: 99}, {key: biff, val: 10}, {key: foo, val: 77]

How can I generate my desired data structure? The following code doesn't seem to append values to the value array.

var d = {}



for (var i in input) {

    var datum = input[i];

    d[datum.key] = datum.val

}