This is an implementation of timestamp key-value store that allows historical record of values inserted for a key in a db. This implementation uses a sorted set of timestamps to make sure that the db meets its constraints.

timestampdb.js

class TimeStampDB{
    constructor (){
        this.db = {}
    }

    set(key, timestamp, value){
        this.db[key] = this.db[key] || {}
        this.db[key][timestamp] = value
        this.db[key]['timestamps'] = this.db[key]['timestamps'] || []
        // find insert position for sorted set of timestamps array
        const position = this.binary_search(timestamp, this.db[key]['timestamps'], 0, this.db[key]['timestamps'].length )
        // convert timestamps to set so as de-duplicate timestamps
        this.db[key]['timestamps'] = Array.from(new Set(this.db[key]['timestamps'].slice(0, position).concat([timestamp]).concat(this.db[key]['timestamps'].slice(position))))
    }

    get(key, timestamp = null){
       
        if(!this.db[key]){
            throw new Error('Key does not exist')
        }

        if(!timestamp){
            // return the last timestamp item inserted into db when timestamp isn't provided
            return this.db[key][this.db[key]['timestamps'][ this.db[key]['timestamps'].length -1]]
        }

        if(this.db[key][timestamp]){
            return this.db[key][timestamp]
        }
        
        const next_greater = this.binary_search(timestamp, this.db[key].timestamps, 0, this.db[key].timestamps.length)
        return this.db[key][this.db[key]['timestamps'][next_greater - 1]]
    }


    binary_search(item, array, start = 0, end = 4){
        let mid = Math.floor((end + start) / 2)
        if(start >= end){
            return start
        }

        if(array[mid] == item) {
            return mid
        }

        if(item < array[mid]){
            return this.binary_search(item, array, start, mid)
        } 
        else if(item > array[mid]){
            return this.binary_search(item, array, mid+1, end)
        }
        
    }
}