简单的 Javascript 碰撞检测？

//DOCUMENT-READY==========================
$(document).ready(function() {
  //VARS----------------------------------
  var step = 10;
  var health = 100;
  
  //MAP-----------------------------------
  var map = [
    [0,1,0,0,0,1,0,0],
    [0,1,0,0,0,1,0,0],
    [0,1,0,0,0,1,0,0],
    [0,1,1,1,0,1,0,0],
    [0,0,0,0,0,0,0,2]
  ];
  
  //DRAW MAP------------------------------
  (function() {
    var tile = "";
    for (var y=0,county=map.length; y<county; ++y) {
      $("#canvas").append('<div class="tile-row" id="row_'+(y+1)+'"></div>');
      for (var x=0,countx=map[y].length; x<countx; ++x) {
        switch (parseInt(map[y][x])) {
          case 0: tile="air"; break;
          case 1: tile="block"; break;
          case 2: tile="spike"; break;
          default: tile="error";
        }
        $("#row_"+(y+1)).append('<div class="tile '+tile+'"></div>');
      }
    }
  })();
  
  //SET BOUNDARIES------------------------
  var xMin=$("#canvas").offset().left, xMax=xMin+$("#canvas").width()-$("#player").width();
  var yMin=$("#canvas").offset().top, yMax=yMin+$("#canvas").height()-$("#player").height();
  
  //PLACE PLAYER--------------------------
  $("#player").css("left",xMin).css("top",yMin);
  
  //MOVE PLAYER---------------------------
  $(document).keydown(function(e){
    var player=document.getElementById("player"), tile=null;
    var x=$(player).offset().left, playerLeft=x, playerRight=playerLeft+$(player).width();
    var y=$(player).offset().top, playerTop=y, playerBottom=playerTop+$(player).height();
    
    function checkCollision(playerCorner1x, playerCorner1y, playerCorner2x, playerCorner2y) {
      var collisionTiles=["block","spike"];
      //check if the front of the player is colliding with the environment
      var front = (playerCorner1x==playerCorner2x?playerCorner1x:playerCorner1y);
      var corner1 = (front==playerCorner1x?playerCorner1y:playerCorner1x);
      var corner2 = (front==playerCorner1x?playerCorner2y:playerCorner2x);
      //check every pixel along the front for collision
      for (var i=corner1; i<corner2; ++i) {
        var checkTile = document.elementFromPoint((front==playerCorner1x?front:i), (front==playerCorner1y?front:i));
        if (collisionTiles.indexOf(checkTile.className.split(" ")[1]) != -1) {
          if ($(checkTile).hasClass("spike")) {console.log("YOU DEAD!");}
          else if ($(checkTile).hasClass("block")) {return checkTile;}
          break;
        }
      }
    }
    
    if(e.which==37 || e.which==65){ //LEFT,A
      x -= step;
      if (x <= xMin) {x = xMin;}
      else {tile = checkCollision(playerLeft-step,playerTop, playerLeft-step,playerBottom);}
      $(player).css("left",(tile?$(tile).offset().left+$(tile).width():x));
    }
    if(e.which==39 || e.which==68){ //RIGHT,D
      x += step;
      if (x >= xMax) {x = xMax;}
      else {tile = checkCollision(playerRight+step,playerTop, playerRight+step,playerBottom);}
      $(player).css("left",(tile?$(tile).offset().left-$(player).width():x));
    }
    if(e.which==38 || e.which==87){ //UP,W
      y -= step;
      if (y <= yMin) {y = yMin;}
      else {tile = checkCollision(playerLeft,playerTop-step, playerRight,playerTop-step);}
      $(player).css("top",(tile?$(tile).offset().top+$(tile).height():y));
    }
    if(e.which==40 || e.which==83){ //DOWN,S
      y += step;
      if (y >= yMax) {y = yMax;}
      else {tile = checkCollision(playerLeft,playerBottom+step, playerRight,playerBottom+step);}
      $(player).css("top",(tile?$(tile).offset().top-$(player).height():y));
    }
  });
});

div {margin:0; padding:0; border-style:none; box-sizing:border-box; overflow:hidden;}

/*CANVAS================*/
#canvas {display:inline-block;}

/*TILES=================*/
.tile-row {width:100%; height:40px;}
.tile {float:left; width:40px; height:100%;}
.tile.air {background-color:skyblue;}
.tile.block {background-color:sienna;}
.tile.spike {background-color:gray;}
.tile.error {background-color:red;}

/*PLAYER================*/
#player {position:absolute; width:15px; height:15px; background-color:black;}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<div id="canvas"></div>
<div id="player"></div>