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Comment by shp0ngle | Hacker News Reader

I do not undetstand the async example. What is the difference between

      try {
        const response = await fetch(url);
        const text = await response.text();
        element.textContent = text;
      } catch (error) {
        element.textContent = error.message;
      } finally {
        hideLoadingSpinner();
      }

and

      try {
        const response = await fetch(url);
        const text = await response.text();
        element.textContent = text;
      } catch (error) {
        element.textContent = error.message;
      }
      hideLoadingSpinner();

Other than that, this is great. But I don't understand the async/await version

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In this case, if the error object is undefined/null, then error.messsage throws a TypeError, and the spinner is not hidden.

In general the finally { ... } block is useful because it is guaranteed to execute after the try/catch (if the program has not exited), where as the next line after the try/catch is not, e.g., the try/catch returns, or the catch block throws.

If that's what the example is showing, then it's just obscuring two unrelated try/catch blocks. One for the outcome of the request, and one for the uncertainty of the element reference.

Example:

(()=>{try {return 42} finally {console.log('you will see this')}})()

The fn body returns 3, but also the "finally" executes first and you get the console.log. Same with:

(()=>{try {throw 42} finally {console.log('you will see this')}})()

If "element" is undefined or null, the catch clause will raise an exception. In the first example, hideLoadingSpinner() will be called anyway, while in the second one it won't.

If "element.textContent = error.message" throws an error, "hideLoadingSpinner()" won't get called (in the second example).

Finally blocks ensure code executes even on exception. In the second example hideLoadSpinner will never get called if you hit the catch block

That's wrong- if the catch block runs without throwing any exceptions of its own then hideLoadSpinner will be called.

incorrect

     try {
        throw new Error("catch me !"); // force try to fail
      } catch (catchedError) {
        console.log("inside catch");
        // throw new Error("hmm");
      } finally {
        // always executed         
        console.log("inside finally");
      }
      // always executed
      console.log("after try catch finally");

the finally statement can be useful when another error is thrown inside the catch block, in which case you have more serious problems in your code

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