gistfile1.txt

const backingObject = Symbol();
const prune = Symbol();
const FIVE_MINUTES = 1000 * 60 * 5;

function getTimestamp() {
    return (new Date()).getTime();
}

// Example usage:
// const inst = new SimpleReporting();
// inst.record(0);
// inst.record(3);
// console.log(inst.mean()) // return 1.5
class SimpleReporting {
    constructor() {
        this[backingObject] = {};
    }
    
    record(val) {
        if (typeof val !== 'number') {
            throw new Error(`${val} is not a number!`);
        }
        const timestamp = getTimestamp();
        this[prune](timestamp)
        if (this[backingObject][timestamp]) {
            this[backingObject][timestamp].push(val);
        } else {
            this[backingObject][timestamp] = [val];
        }
    }

    mean() {
        this[prune](getTimestamp());
        let num = 0;
        let denom = 0;
        Object.keys(this[backingObject]).forEach(key => {
           num += this[backingObject][key].reduce((prev, curr) => {
               denom += 1;
               return prev + curr;
           }, 0); 
        });
        return (num / denom);
    }
    
    [prune](timestamp) {
        // TODO: currently, memory is more than twice the size of the data, but that may not always
        // be the case -- someday, we should prune in place.
        // TODO: We prune when we may not need to -- check to see if there are too many keys before
        // pruning, and guard in mean.
        const newBackingObj = {};
        Object.keys(this[backingObject]).forEach(key => {
           if (key >= (timestamp - FIVE_MINUTES)) {
               newBackingObj[key] = this[backingObject][key];
           } 
        });
        this[backingObject] = newBackingObj;
    }
}