Reading and Handling Errors

Errors are useful feedback. A syntax error means the source cannot be parsed; a ReferenceError often means a name is unavailable; a TypeError often means an operation is invalid for a value. Application errors can also represent validation failures, missing records, or failed network requests.

try {
  const value = JSON.parse('{"active": true}');
  console.log(value.active);
} catch (error) {
  console.error("The supplied JSON is invalid.", error);
}

Use try...catch around operations that may throw and where your code can take a useful action, such as displaying a clear message or logging diagnostic details. Do not hide errors with an empty catch block.

Throw meaningful errors#

function divide(a, b) {
  if (b === 0) {
    throw new Error("The divisor must not be zero.");
  }
  return a / b;
}

Use the built-in Error type for ordinary errors. Custom error classes can be useful when callers need to distinguish between error categories.

Validate at boundaries#

Check external input before using it. Data from forms, URLs, storage, and HTTP APIs should be treated as untrusted or potentially malformed. A valid JSON document can still have the wrong shape or values for your application.

Practice#

Wrap JSON.parse in error handling and show a user-friendly message when the input is invalid. Keep technical details available for debugging without exposing secrets.