Error Handling

Quick Reference

Concept	Description
`try...catch...finally`	Handles runtime errors, ensures cleanup.
`throw`	Manually trigger errors.
Error Object	Includes `name`, `message`, `stack`.
Error Types	`TypeError`, `ReferenceError`, `SyntaxError`, etc.
Sync Errors	Caught by `try...catch`.
Async Errors	Not caught unless inside `async` function or handled via `.catch()`.

`try...catch...finally` Syntax

try...catch works only for synchronous errors.
Use finally for cleanup tasks.
Always log errors (error.message, error.stack) for debugging.

try {
  console.log(x); // ReferenceError: x is not defined
} catch (err) {
  console.error(err.message);
} finally {
  console.log("Cleanup done");
}

Throwing Errors

Prefer throw new Error("message") over throw "message" for consistency and debugging.

function divide(a, b) {
  if (b === 0) {
    throw new Error("Cannot divide by zero");
  }
  return a / b;
}

try {
  console.log(divide(10, 0));
} catch (err) {
  console.error(err.message);
}

Built-in Error Types

Type	Example
`Error`	`throw new Error("Custom error")`
`SyntaxError`	`eval("foo bar")`
`ReferenceError`	`console.log(x)` (x is undefined)
`TypeError`	`null.foo()`
`RangeError`	`new Array(-1)`
`URIError`	`decodeURIComponent("%")`

Identify error types to diagnose issues faster.
Avoid unnecessary eval() usage to prevent SyntaxError.

Handling Async Errors

Inside async function (try...catch)

async function fetchData() {
  try {
    let res = await fetch("<https://api.example.com/data>");
    let data = await res.json();
    console.log(data);
  } catch (err) {
    console.error("Error:", err);
  }
}

Async errors in callbacks are not caught

try {
  setTimeout(() => { throw new Error("Not caught"); }, 1000);
} catch (err) {
  console.error("Won't be caught:", err);
}

Fix: Handle inside the callback

Quick Reference

try...catch...finally Syntax

Throwing Errors

Built-in Error Types

Handling Async Errors

`try...catch...finally` Syntax