be careful with .forEach()

I finally got around to solving one of the toy problems that I couldn't completely solve in the pre-course the diagnostics.

My issue was that I didn't understand the behaviors of .forEach() loops.

I was expecting a return statement to break out of the loop, but that's not what .forEach() is for. forEach() is used when you want to iterate over all of the items in your array. 'Return' in this case only breaks out of the current function but the loop resumes. The only way to break out of .forEach() loops is to throw an exception.

Instead of using .forEach(), in this case, a better tool is a simple for or while loop. These lend themselves perfectly for catching certain cases and then, for instance, returning out of them.

I'll show the buggy code first and then my work-around (storing the a boolean in a variable). If I was re-factoring this, I would ditch the .forEach() in favor of a 'for' loop.

Broken:

var isIPv4Address = function(inputString){

  var ip4 = inputString.split('.')
  ip4 = ip4.filter(item => item !== '')
  ip4 = ip4.map(item => Number(item)).filter(item => String(item) !== 'NaN')

  if (ip4.length !== 4) return false


  ip4.forEach(function(item){
    if (item > 255) {
    return false
  })
}
var a = '213.234.234.344'
console.log(isIPv4Address(a))

Working:

var isIPv4Address = function(inputString){

  var isAddress = true;

  var ip4 = inputString.split('.')
  ip4 = ip4.filter(item => item !== '')
  ip4 = ip4.map(item => Number(item)).filter(item => String(item) !== 'NaN')

  if (ip4.length !== 4) isAddress = false

  ip4.forEach(function(item){
    if (item > 255) isAddress = false
  })

  return isAddress
}
var a = '203.294.234.234'
console.log(isIPv4Address(a))