unspiral.js

const roundNum = (i, j) => Math.max(Math.abs(i), Math.abs(j))

const sumRange = n => (n * (n + 1)) / 2
const accumulateBy = f => n => f(sumRange(n))

const roundCircumference = n => 8 * n
const accumulateDistanceUpToRound = accumulateBy(roundCircumference)

const distanceOnOuterRound = (i, j) => {
  const n = roundNum(i, j)
  
  const [ moveRight, moveDown, moveLeft, moveUp ] =
        [ n + j,     n + i,    n - j,    n - i  ]

  const topRightTurn = moveRight + moveDown
  const bottomLeftTurn = moveLeft + moveUp

  const fullTopRightTurn = 4 * n
  const isTargetOnTopRightArea = i < j
  
  return isTargetOnTopRightArea
          ? topRightTurn
          : fullTopRightTurn + bottomLeftTurn
}


export const unspiral = (i, j) => {
  const n = roundNum(i, j)
  return accumulateDistanceUpToRound(n - 1) + distanceOnOuterRound(i, j)
}

I really like the naming of the variables in distanceOnOuterRound; it looks very clear what is going on.

However I think the name roundOf is not self-descriptive yet.

Ummmm, This is a tricky one. How about just roundNum ?