Handling Errors

Errors are thrown (and should be thrown by you) when a non-happy path is encountered in your code. For example:

• Data received from an API is not in the expected format
• The connection to a database is lost
• A user tries to log in with an incorrect password

Like Python, when an error is thrown, JavaScript yeets the program out of its current context and into the nearest try/catch block, or, if there isn't one, it crashes the program. For example:

const titan = {};
console.log(titan.neck.thickness);
console.log("done");

The code above prints:

TypeError: Cannot read properties of undefined (reading 'thickness')

It never gets to the console.log("done") because the error crashes the program. But what if we use a try/catch block? We place the potentially error-throwing code in the try block, and if an error is thrown, execution immediately jumps to the catch block (ignoring any code in the try block that hasn't run yet):

try {
  const titan = {};
  console.log(titan.neck.thickness);
  console.log("what's a titan?");
} catch (err) {
  console.log(err.message);
}
console.log("done");

Which prints:

Cannot read properties of undefined (reading 'thickness')
done