generator-like range, using Proxy.

rangeProxy.js

function fakeGen (fromV = 0, toV, step = 1) {
  // only one arg
  if (toV == undefined) {
    toV = fromV
    fromV = 0
  }

  // init status
  const status = {
    done: false,
    value: fromV - step
  }

  function setStatusDone () {
    status.value = undefined
    status.done = true
    nextFn = () => status
  }

  function nextFn () {
    // prevent infinite range
    if ((toV - fromV) * step < 0) {
      setStatusDone()
    }
    
    else {
      nextFn = () => {
        if (!status.done) {
          status.value += step

          if (status.value >= toV) {
            setStatusDone()
          }
        }

        return status
      }
    }

    return nextFn()
  }
  
  return new Proxy(
    // nothing in the instance of generator
    {},
    {
      get (target, key, receiver) {
        if (key === 'next') {
          return nextFn
        }
        
        return target[key]
      }
    }
  )
}

// examples 

const g = fakeGen(1, 4)
g.next() // { done: false, value: 1 }
g.next() // { done: false, value: 2 }
g.next() // { done: false, value: 3 }
g.next() // { done: true, value: undefined }

//---------------

const g = fakeGen(3)
g.next() // { done: false, value: 0 }
g.next() // { done: false, value: 1 }
g.next() // { done: false, value: 2 }
g.next() // { done: true, value: undefined }

//---------------

const g = fakeGen(1, 10, 3)
g.next() // { done: false, value: 1 }
g.next() // { done: false, value: 4 }
g.next() // { done: false, value: 7 }
g.next() // { done: true, value: undefined }

//---------------

const g = fakeGen(1, 10, -1) // infinite gen wont work
g.next() // { done: true, value: undefined }