rangeClass.js

// Build a class to represent a range of numbers that has:

// a beginning index
// an end index (optional). If there is no end index, the range should include only the passed-in start value.
// a ‘step’ (optional)
// it should not store the range as an array of numbers; it should work in constant space.
// The step is the interval at which elements are included. For instance, a step of 1 includes every element in the range, while a step of 2 includes every other element.

// You should allow a negative value for ‘step’ to count backwards. If no step is provided and the start is more than the end, assume we’re counting backwards.

// The range should have a constructor that accepts these arguments in this order:

// beginning index
// end index
// step interval
// It should also support the following utility functions:

// size(): return the number of items represented by the range
// each(callback(index)): iterate over the range, passing each value to a callback function
// includes(index): return whether or not the range includes the passed value
// You should also be aware of the following caveats:

// Should return null if we are given no ‘start’ value.
// Again, Range should use constant space, even during the each() method, * i.e. you should not use an array as backing storage.

var Range = function(start, end, step) {
  this.start = start || null;
  this.end = end || 1;
  this.step = step || 1;
};

Range.prototype.size = function () {
  var count = 0;
  if(this.start > this.end || this.step < 0){
    for(var i = this.start; i >= 0; i -= Math.abs(this.step)){
      count++;
    }
  }
  else{
    for(var i = this.start; i <= this.end; i += this.step){
      count++;
    }
  }
  
  return count;
};

Range.prototype.each = function (callback) {
  if(this.start > this.end || this.step < 0){
    for(var j = this.start; j >= 0; j -= Math.abs(this.step)){
      callback(j);
    }
  }
  else{
    for(var j = this.start; j <= this.end; j += this.step){
      callback(j);
    }
  }
};

Range.prototype.includes = function (val) {
  if(this.start > this.end || this.step < 0){
    for(var k = this.start; k >= 0; k -= Math.abs(this.step)){
      if(k === val){
        return true;
      }
    }
    return false;
  }
  else{
    for(var k = this.start; k <= this.end; k += this.step){
      if(k === val){
        return true;
      }
    }
    return false;
  }
};