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Learn JavaScript: Error Handling
Handling with try...catch

In the previous exercise we caught an error that we threw, but we can also use a try...catch statement to handle built-in errors that are thrown by the JavaScript engine that is reading and evaluating our code.

const someVar = 'Cannot be reassigned'; try { someVar = 'Still going to try'; } catch(e) { console.log(e); } // Prints: TypeError: Assignment to constant variable.

In the example above, we didn’t use the throw keyword to throw a custom error, rather we tried to re-assign a const variable and a TypeError was thrown. Then, in our catch block, we logged the error to the console.

Using a try...catch statement for built-in JavaScript errors is really beneficial when we need to use data from an external source that’s not written directly in our program.

Let’s say we expect to grab an array from a database but the information we get back is a string. In our program, we could have a function that only works on arrays. If that function was called with a string instead of an array we would get an error and our program would stop running!

However, we can use a try...catch statement to handle the thrown error for us which allows our program to continue running and we receive a message knowing what went wrong! Let’s see how we can implement this in our code.

Instructions

1.

In main.js there is a function capAllElements() that takes an array of elements and capitalizes each element.

Currently, it’s written in a way the function will execute regardless of what argument is passed in but if the argument isn’t an array, an error is thrown and our program stops running. Run your code to see what error shows up in the console.

Let’s handle that error:

  • Put the existing arr.forEach(...) code in a try block.
  • Add a catch statement after the try block and inside the catch block log the error to the console.
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