update array

updateArray.js

function updateArray (arr, newArr) {
    if (!arr.index)
        arr.index = arr.reduce(function(seed, item) {
            seed[item.id] = item
            return seed
        }, {})

    newArr.forEach(function(item) {
        if (arr.index[item.id])
            return _.assign(arr.index[item.id], item)

        arr.index[item.id] = item
        arr.push(item)
    })
}