目前我的jsfiddle允许用户一次输入一些考试成绩，一个数字，并显示这些数字的平均分和总分。当前，如果他们在框中输入-999，这意味着他们已经完成了数字输入，可以计算平均值和总数。

如何编辑它，以便当用户第一次输入-999时，显示“未输入分数”？

<script>

function userInput() {

  var examScores = 0;
  var totScores = 0;
  var i = 0;
  var scores = [];

  while (true) {
    examScores = parseInt(prompt("Enter a score or enter -999 when you're finished: "));

    if (examScores === -999 && scores.length === 0) {
      document.getElementById("scores").innerHTML = "No score entered.";
      break;
    }

    else if (examScores === -999) {
      break;
    }

    else {
      scores.push(examScores);
      i++;
    }
  }

  for(var i = 0; i < scores.length; i++) {
    totScores = totScores + scores[i];
  }

  document.getElementById("scores").innerHTML = "<h1> The sum of these scores is: "+totScores.toFixed(2)+"<br/> The average of these scores is: "+(totScores/scores.length).toFixed(2);
}

</script>

<h1>Exam Scores</h1>
<h3>Click to enter scores</h3>
<input type="button" value="Enter student scores" onclick="userInput()" />
<div id="scores"></div>

顺晟科技：

您需要返回而不是中断循环。

<script>

function userInput() {

  var examScores = 0;
  var totScores = 0;
  var i = 0;
  var scores = [];

  while (true) {
    examScores = parseInt(prompt("Enter a score or enter -999 when you're finished: "));

    if (examScores === -999 && scores.length === 0) {
      document.getElementById("scores").innerHTML = "No score entered.";
      break;
    }

    else if (examScores === -999) {
      break;
    }

    else {
      scores.push(examScores);
      i++;
    }
  }

  for(var i = 0; i < scores.length; i++) {
    totScores = totScores + scores[i];
  }

  document.getElementById("scores").innerHTML = "<h1> The sum of these scores is: "+totScores.toFixed(2)+"<br/> The average of these scores is: "+(totScores/scores.length).toFixed(2);
}

</script>

<h1>Exam Scores</h1>
<h3>Click to enter scores</h3>
<input type="button" value="Enter student scores" onclick="userInput()" />
<div id="scores"></div>

单独打破循环将导致函数继续执行，因此总是到达

<script>

function userInput() {

  var examScores = 0;
  var totScores = 0;
  var i = 0;
  var scores = [];

  while (true) {
    examScores = parseInt(prompt("Enter a score or enter -999 when you're finished: "));

    if (examScores === -999 && scores.length === 0) {
      document.getElementById("scores").innerHTML = "No score entered.";
      break;
    }

    else if (examScores === -999) {
      break;
    }

    else {
      scores.push(examScores);
      i++;
    }
  }

  for(var i = 0; i < scores.length; i++) {
    totScores = totScores + scores[i];
  }

  document.getElementById("scores").innerHTML = "<h1> The sum of these scores is: "+totScores.toFixed(2)+"<br/> The average of these scores is: "+(totScores/scores.length).toFixed(2);
}

</script>

<h1>Exam Scores</h1>
<h3>Click to enter scores</h3>
<input type="button" value="Enter student scores" onclick="userInput()" />
<div id="scores"></div>

由于上面的行正在执行，您自己的工作将被覆盖。从循环内返回将结束函数的执行。