Take a Ten Minute Walk (JavaScript)

You live in the city of Cartesia where all roads are laid out in a perfect
grid. You arrived 10 minutes too early to an appointment, so you decided
to take the opportunity to go for a short walk. 

The city provides its citizens with a Walk Generating App on their phones
-- every time you press the button it sends you an array of one-letter
strings representing directions to walk (eg. ['n', 's', 'w', 'e']). 

You always walk only a single block in a direction and you know it takes
you 1 minute to traverse one city block, so create a function that will
return true if the walk the app gives you will take you exactly 10
minutes (you don't want to be early or late!) and will, of course, return
you to your starting point. Return false otherwise.

Note: you will always receive a valid array containing a random assortment
of direction letters ('n', 's', 'e', or 'w' only). It will never give you
an empty array (that's not a walk, that's standing still!).

// 1 block = 1 minute
// if walk = 10 minutes, true
// otherwise false
// must return to starting point
// if paths start with 0 (set equal to 0) we can increment or decrement
// then, if a path ends again with 0, we know it can return true

// ns (north-south) should equal 0 
// we (west-east) should equal 0 

// if the direction is north, north-south add 1 - leaving
// if the direction is south, north-south subtract 1 - coming back
// if the direction is west, west-east add 1 - leaving
// if the direction is east, west-east subtract 1 - coming back

// if the length of the walk is equal to 10 and ns is 0 and we is 0, return the walk length, otherwise return false

function isValidWalk(walk) {
  let ns = 0, we = 0; 
    for (let dir of walk) { 
      if (dir == 'n') ns += 1; 
      if (dir == 's') ns -= 1; 
      if (dir == 'w') we += 1; 
      if (dir == 'e') we -= 1; 
    } 

    return walk.length == 10 && ns === 0 && we === 0; 
}

function isValidWalk(walk) {
  var dx = 0
  var dy = 0
  var dt = walk.length

  for (var i = 0; i < walk.length; i++) {
    switch (walk[i]) {
      case 'n': dy--; break
      case 's': dy++; break
      case 'w': dx--; break
      case 'e': dx++; break
    }
  }

  return dt === 10 && dx === 0 && dy === 0
}

function isValidWalk(walk) {
  function count(val) {
    return walk.filter(function(a){return a==val;}).length;
  }
  return walk.length==10 && count('n')==count('s') && count('w')==count('e');
}

function isValidWalk(walk) {
  const north = walk.filter(item => { return item === "n" }).length;
  const south = walk.filter(item => { return item === "s" }).length;
  const east = walk.filter(item => { return item === "e" }).length;
  const west = walk.filter(item => { return item === "w" }).length;

  return walk.length === 10 && north === south && east === west;
}