try, catch and finally

When something fails

Some operations can fail: reading data that does not exist, converting text to a number, dividing by zero in an invalid way... If you do not handle it, an error stops the program's execution. To handle it in a controlled way you use the try...catch block.

try {
  // code that may fail
  const data = JSON.parse("this is not JSON");
} catch (error) {
  // runs only if there was an error
  console.log("Something went wrong:", error.message);
}

• The try block contains the "risky" code.
• If an error is thrown, control jumps to the catch block, which receives the error object.
• If there is no error, catch is ignored completely.

The finally block

It is optional and runs always, whether there was an error or not. It is used for cleanup tasks (closing connections, hiding a loading indicator...):

try {
  doSomething();
} catch (error) {
  console.log("Error:", error.message);
} finally {
  console.log("This runs no matter what");
}

Examples

Catch an error and continue

function parse(text) {
  try {
    return JSON.parse(text);
  } catch (error) {
    console.log("Invalid JSON:", error.message);
    return null;
  }
}
console.log(parse('{"ok":true}'));
console.log(parse("not json"));