Question

我正在编写一些JavaScript，从1到9中取出9个数字的数组，这些数字不按顺序排列，并以字符串的形式返回10 - 1的倒计时。

例如：

输入： [4,9,3,10,6,8,2,7,1,5];

输出：＆＃34; 10 9 8 7 6 5 4 3 2 1升空！＆＃34;

JavaScript测试：

Test.assertEquals(liftoff([2, 8, 10, 9, 1, 3, 4, 7, 6, 5]),"10 9 8 7 6 5 4 3 2 1 liftoff!")

JavaScript代码：

function liftoff(instructions){

  var countdown = "";
  var start = 10;

  for (start; start >= 1; start--) {

    for (var i = 0; i < instructions.length; i++) {

      if (instructions[i] == start) {
        var count = instructions[i].toString();
        countdown += count + " ";
      }

    }

  }

  countdown += " liftoff!";
  console.log(countdown);
}

我得到的错误：

Expected: 10 9 8 7 6 5 4 3 2 1 liftoff!, instead got: undefined

为什么未定义？

Answer 1

function liftoff(instructions) {
  return instructions
  // sort into correct order
  .sort(function(a, b){
    return b - a;
  })
  // convert into string with spaces
  .join(' ') +
  // add 'lift off!
  ' lift off!';
}

Answer 2

这里还有一个选项可以满足您的需求：

<强> HTML

<!DOCTYPE Html />
<html>
    <head>
        <title></title>
    </head>
    <body>
        <input type="button" value="Countdown" id="btnCountdown"/>
        <script type="text/javascript" src="theJS.js"></script>
    </body>
</html>

<强>的JavaScript

var countdown = document.getElementById("btnCountdown");
var instructions = [5, 3, 2, 6, 4, 1, 9, 7, 8];
countdown.onclick = function () {
    var sortedInstructions = instructions.sort();

    for (var i = instructions.length - 1; i >= 0; i--) {
        var text = document.createTextNode(sortedInstructions[i]);
        var el = document.createElement("P");
        el.appendChild(text);
        document.body.appendChild(el);

        if (i == 0) {
            var liftOff = document.createTextNode("Lift Off!");
            var lastEl = document.createElement("P");
            lastEl.appendChild(liftOff);
            document.body.appendChild(lastEl);
        }
    }
}

JavaScript倒计时循环

2 个答案: