writeNumbers

writeNumbers.js

const writeNumbers = () => {
  const categories = ['scans', 'fatLoss', 'muscleGained']
  // base number is inside span
  // number to increase by is inside data-increase attribute
  const startDate = new Date('Nov 21 2017')
  const now = new Date()
  const difference = now - startDate
  const ms = 1000
  const seconds = 60
  const minutes = 60
  const hours = 24
  const days = 7
  const weeks = difference / ms / seconds / minutes / hours / days

  const removeCommas = str => str.replace(',', '')
  const addCommas = str => {
    // maybe later
  }
  const getNumbers = category => {
    const element = document.querySelector(category)
    return {
      base: element ? parseInt(removeCommas(element.innerText)) : 10,
      increase: element ? parseInt(element.dataset.increase) : 10
    }
  }

  const getCurrentValue = category =>
    parseInt(
      getNumbers(category).base + getNumbers(category).increase * weeks,
      10
    )

  categories.map(category => {
    const element = document.querySelector(category)
    if (!element) return false
    element.innerText = getCurrentValue(category)
  })
}

writeNumbers()