random.js

$(function () {
  var run = 0,
    heading = $("h1"),
    timer;

  $("#start").click(function () {
    var list = $("#list")
      .val()
      .replace(/ +/g, " ")
      .replace(/^ | $/g, "")
      .split(" ");
    if (!run) {
      heading.html(heading.html().replace("吃这个！", "吃什么？"));
      $(this).val("停止");
      timer = setInterval(function () {
        var r = Math.ceil(Math.random() * list.length),
          food = list[r - 1];
        $("#what").html(food);
        var rTop = Math.ceil(Math.random() * $(document).height()),
          rLeft = Math.ceil(Math.random() * ($(document).width() - 50)),
          rSize = Math.ceil(Math.random() * (37 - 14) + 14);
        $("<span class='temp'></span>")
          .html(food)
          .hide()
          .css({
            top: rTop,
            left: rLeft,
            color: "rgba(0,0,0,." + Math.random() + ")",
            fontSize: rSize + "px",
          })
          .appendTo("body")
          .fadeIn("slow", function () {
            $(this).fadeOut("slow", function () {
              $(this).remove();
            });
          });
      }, 50);
      run = 1;
    } else {
      heading.html(heading.html().replace("吃什么？", "吃这个！"));
      $(this).val("不行，换一个");
      clearInterval(timer);
      run = 0;
    }
  });

  document.onkeydown = function enter(e) {
    var e = e || event;
    if (e.keyCode == 13) $("#start").trigger("click");
  };
});