Get points between two points on simple grid (must be in a straight line)

lineMath.js

/**
 * Get points between two points on simple grid. Points must be in a straight line.
 * Results will include start and end points
 * 
 * @param A array x, y coordinates of one point
 * @param B array x, y coordinates of second point
 * @return false if points are not in a straight line or if points are the same else
 *         array of arrays of x, y coordinates between the two points.
 *
 * fixed so that coordinates can be in any direction from each other.
 * http://stackoverflow.com/questions/13491676/get-all-pixel-coordinates-between-2-points
 * http://jharaphula.com/javascript-function-to-find-all-points-between-any-two-points/
 */
var lineMath = function(A, B){
    
  A = [Number(A[0]), Number(A[1])];
  B = [Number(B[0]), Number(B[1])];

  // if points are the same, return the point    
  if(A[0] == B[0] || A[1] == B[1]){
    return A;
  }
  
  // if points are not in a straight line, return (bool) false
  if(Math.abs(A[0] - B[0]) == Math.abs(A[1] - B[1])){
      return false;
  }
    
  function slope(a, b) {
    if (a[0] == b[0]) {
      return null;
    }
    return (b[1] - a[1]) / (b[0] - a[0]);
  }

  function intercept(point, slope) {
    if (slope === null) {
      // vertical line
      return point[0];
    }
    return point[1] - slope * point[0];
  }

  var m = slope(A, B);
  var b = intercept(A, m);
  
  var swapped = false;
  if (A[0] > B[0] || A[1] > B[1]){
    var A2, B2;
    swapped = true;
    B2 = [A[0], A[1]];
    A2 = [B[0], B[1]];
    A = A2; B = B2;
  }

  var coordinates = [];
  var y;
  if(A[0] != B[0]){
    if(A[0] < B[0]){
      for (x = A[0]; x <= B[0]; x++) {
        y = m * x + b;
        coordinates.push([x, y]);
      }      
    }else{
      for (x = A[0]; x >= B[0]; x--) {
        y = m * x + b;
        coordinates.push([x, y]);
      }       
    }
  }else{
    for (y = A[1]; y <= B[1]; y++) {
      coordinates.push([A[0], y]);
    }    
  }

  if(swapped)
    coordinates.reverse();
    
  return coordinates;
}

qunit.lineMath.js

/** out */

QUnit.test( "lineMath 0 degree", function( assert ) {
  var A = [0,2], B = [0,0];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [0,1], B] );
});

QUnit.test( "lineMath 45 degree", function( assert ) {
  var A = [0,2], B = [2,0];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [1,1], B] );
});

QUnit.test( "lineMath 90 degree", function( assert ) {
  var A = [0,2], B = [2,2];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [1,2], B] );
});

QUnit.test( "lineMath 135 degree", function( assert ) {
  var A = [0,2], B = [2,4];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [1,3], B] );
});

/** in **/

QUnit.test( "lineMath 180 degree", function( assert ) {
  var A = [0,0], B = [0,2];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [0,1], B] );
});

QUnit.test( "lineMath 225 degree", function( assert ) {
  var A = [2,0], B = [0,2];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [1,1], B] );
});

QUnit.test( "lineMath 270 degree", function( assert ) {
  var A = [2,2], B = [0,2];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [1,2], B] );
});

QUnit.test( "lineMath 315 degree", function( assert ) {
  var A = [2,4], B = [0,2];
  var coords = lineMath(A, B);
  assert.deepEqual( coords, [A, [1,3], B] );
});