setInterval函数返回undefined(setInterval function returning undefined)

setInterval函数返回undefined(setInterval function returning undefined)

我是第一次在JavaScript中学习setInterval，我试图在5秒后显示一个值。 我的代码如下：

<button onclick="myTest()">Try it</button> <script> function myTest() { const ret = myFunction(); alert(ret); } function myFunction() { let i = 0; const interval = setInterval(function(){ i += 1; if (i === 5) { clearInterval(interval); return i; } }, 1000); } </script>

我希望5被警告，而不是我undefined 。 有谁知道为什么会这样？ 提前致谢！

I am learning setInterval in JavaScript for the first time, and am trying to show a value after 5 seconds. My code is given below:

<button onclick="myTest()">Try it</button> <script> function myTest() { const ret = myFunction(); alert(ret); } function myFunction() { let i = 0; const interval = setInterval(function(){ i += 1; if (i === 5) { clearInterval(interval); return i; } }, 1000); } </script>

I want 5 to be alerted, instead I am getting undefined. Does anyone know why this is happening? Thanks in advance!

最满意答案

您无法从setInterval调用中的匿名函数返回任何内容。 您需要从该函数内写入console 。 尝试这个：

function myTest() {
  // this function is now redundant - you could call myFunction() directly
  myFunction();
}

function myFunction() {
  let i = 0;
  const interval = setInterval(function() {
    i += 1;
    if (i === 5) {
      clearInterval(interval);
      console.log(i); // this will appear after 5 seconds...
    }
  }, 1000);
}

myTest(); 
  
 
You can't return anything from the anonymous function within the setInterval call. You need to write to the console from within that function. Try this:
 
 
 
  
  
function myTest() {
  // this function is now redundant - you could call myFunction() directly
  myFunction();
}

function myFunction() {
  let i = 0;
  const interval = setInterval(function() {
    i += 1;
    if (i === 5) {
      clearInterval(interval);
      console.log(i); // this will appear after 5 seconds...
    }
  }, 1000);
}

myTest();