javascript - Try catch block is not catching nested callbacks - Stack Overflow

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I'm trying to understand how to use try/catch when it es to nested callbacks. Why doesn't this piece of code catch my new error ?

function test(cb) {
  setTimeout(function() {
    throw new Error("timeout Error");
  }, 2000);
}

try {
  test(function(e) {
    console.log(e);
  });
} catch (e) {
  console.log(e);
}

I'm trying to understand how to use try/catch when it es to nested callbacks. Why doesn't this piece of code catch my new error ?

function test(cb) {
  setTimeout(function() {
    throw new Error("timeout Error");
  }, 2000);
}

try {
  test(function(e) {
    console.log(e);
  });
} catch (e) {
  console.log(e);
}

• javascript

Share Improve this question Follow edited Oct 21, 2016 at 14:16 user3589620 asked Oct 21, 2016 at 14:05 runners3431runners3431 1,45511 gold badge1313 silver badges3131 bronze badges

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2 Answers 2

Sorted by: Reset to default 10

The error happens asynchronously, when the function passed to setTimeout runs. By the time the error is thrown, the test function has already finished executing.

There are many ways to set a timer for Javascript execution. Here's one way that uses Promise.race():

(async () => {
  try {
    await Promise.race([

      // Timer.
      new Promise((res, rej) => {
        setTimeout(() => {
          rej("Timeout error!");
        }, 2000);
      }),

      // Code being timed.
      new Promise((res, rej) => {
        // Do some stuff here.
        // If it takes longer than 2 seconds it will fail.
        res("Finished in under 2 seconds.");
      })

    ]);
  } catch (err) {
    console.log("we got an err: " + err);
  }
})();

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