Question

我想知道只有在通过时才“做某事”，就像catch仅在出现错误时才运行。就像在我的示例中一样，console.log("FOO")不会导致错误，因此捕获将不会运行，但是如果没有捕获，我该如何运行 only ？

 try { 
  console.log("FOO")
 }
 catch(err) {
   message.innerHTML = "Input is WRONG";
 }
 message.innerHTML = "Input Works!" // <--- this will always get hit regardless of error or not

Answer 1

要使捕获运行，try块必须失败-就像缺少变量一样。

const messageA = document.querySelector('#message-a');
const messageB = document.querySelector('#message-b');

const a = 10;
const b = 10;  
// const c = 10;
 

//  Test 1 (works)
try {
  let sum = a + b;
  messageA.innerHTML = "We're Happy!"
} catch (err) {
  messageA.innerHTML = "Houston we have a problem!";
}

//  Test 2 (fails because c is not defined)
try {
  let sum = a + c;
  messageB.innerHTML = "We're Happy!"
} catch (err) {
  messageB.innerHTML = "Houston we have a problem!";
}

<p>Test 1: <span id="message-a"></span></p>
<p>Test 2: <span id="message-b"></span></p>

if / else和try / catch之间的区别

如果/其他是评估条件的条件语句，例如x == 42
然后根据结果运行true或false块。

if (condition) { 
    /* condition is true do... */
}
else { 
    /* condition is false do... */ 
}

Try / catch是 exception语句，它将始终运行try块并且仅如果某些东西引发了错误，则将控制权转移到catch块 （通常是致命错误，否则将破坏程序。）

try {
    /* do this... and if it fails transfer control to catch */
} 
catch(err) {
    /* something caused an error now do this... */
}

将其视为处理错误的方法-就像您向api和由于某种原因，服务器没有响应，您没有授权或...

了解详情： Control flow and error handling on MDN

Answer 2

我认为您可能需要这样的东西：

var success = true;
try { 
    console.log("FOO");
}
catch(err) {
    success = false;
}
if (success)
    message.innerHTML = "Input Works!";
else
    message.innerHTML = "Input is WRONG";

如果未运行Catch，如何显示内容？

2 个答案: