Question

未捕获的类型错误：无法读取 null 的属性“toLowerCase”

2016-04-28

22103

javascript

在我更新其他 javascript 之前，此提示一直运行良好。我不知道我是怎么搞砸它的。此函数在 body 标签中声明为运行“onload”。

function funcPrompt() {
   var answer = prompt("Are you a photographer?", "Yes/No");
   answer = answer.toLowerCase();

if (answer == "yes") {
    alert('Excellent! See our links above and below to see more work and find contact info!');
}
else if(answer == "no") {
    alert('That is okay! See our links above and below to learn more!');
}
else if(answer == null || answer == "") {
    alert('Please enter an answer.');
    funcPrompt();
}
else {
    alert('Sorry, that answer is not an option');
    funcPrompt();
}
}

现在我突然收到此错误，并且提示不会出现。

Answer 1

不确定为什么会得到 null，但是如果您想避免 null，请使用以下命令：

answer = (answer?answer:'').toLowerCase();

Answer 2

如果我们点击 取消 ，提示将返回 null ，并且不能对 null 应用 toLowerCase （将导致异常！）

在所有其他条件之前添加条件 answer===null ，然后 return 以停止 函数 的执行

function funcPrompt() {
  var answer = prompt("Are you a photographer?", "Yes/No");
  if (answer === null || answer === "") {
    alert('Please enter an answer.');
    funcPrompt();
    return;
  }
  answer = answer.toLowerCase();
  if (answer == "yes") {
    alert('Excellent! See our links above and below to see more work and find contact info!');
  } else if (answer == "no") {
    alert('That is okay! See our links above and below to learn more!');
  } else {
    alert('Sorry, that answer is not an option');
    funcPrompt();
  }
}
funcPrompt();

Answer 3

对于您来说，最好使用确认而不是提示

function funcConfirm() {
  var answer = confirm("Are you a photographer?");

  if (answer === true) {
    alert('Excellent! See our links above and below to see more work and find contact info!');
  } else {
    alert('That is okay! See our links above and below to learn more!');
  }
}

funcConfirm();