References

Beginner-friendly references for web development, with live, editable examples.

The JavaScript throw statement

Statement JavaScript All modern browsers Updated
Quick answer

The throw statement raises an error, stopping the current execution and jumping to the nearest catch block (or crashing if there isn't one). Throw an Error object: throw new Error("message"). It's how you signal that something went wrong so calling code can handle it.

Overview

throw raises an error on purpose. When you hit a situation your code can't handle — invalid input, a failed precondition, a missing resource — you throw to signal failure. Execution stops immediately and control jumps to the nearest enclosing catch block; if there isn't one, the error propagates up and, unhandled, crashes that code path.

You can technically throw any value, but you should throw an Error object: throw new Error("Amount must be positive"). Error objects carry a message and a stack trace, which makes debugging far easier than throwing a bare string. There are built-in error types — TypeError, RangeError — and you can subclass Error for your own.

It works hand in glove with try...catch: throw raises, catch handles. In an async function, a throw becomes a rejected promise, caught by try...catch around the await. Throw for exceptional conditions, not ordinary control flow — for an expected "not found", returning null or a result object is usually cleaner than throwing.

Syntax

throw new Error("Something went wrong");

function withdraw(amount) {
  if (amount <= 0) {
    throw new Error("Amount must be positive");
  }
  // ...
}

Example

Live example 
<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  function half(n) {
    if (typeof n !== 'number') throw new Error('not a number');
    return n / 2;
  }

  const results = [];
  for (const input of [10, 'oops']) {
    try { results.push(half(input)); }
    catch (e) { results.push('error: ' + e.message); }
  }

  document.getElementById('out').textContent = results.join('\n'); // 5 / error: not a number
</script>

Best practices

  • Throw an Error object (new Error(msg)), not a plain string — it carries a stack trace.
  • Use specific built-in types like TypeError or RangeError where they fit.
  • Pair every throw with a try...catch somewhere up the call chain.
  • Reserve throwing for exceptional cases; return a value for expected outcomes like "not found".

Frequently asked questions

How do I throw an error in JavaScript?
Use throw new Error("message"). Execution stops and jumps to the nearest catch block.
Should I throw a string or an Error?
An Error object. It includes a message and a stack trace, which a plain string lacks, making errors much easier to debug.
What happens if a thrown error isn't caught?
It propagates up the call stack and, if never caught, stops that execution path (and logs an uncaught error).
How does throw work with async/await?
In an async function, a throw rejects the returned promise. Catch it with try...catch around the await.
this try...catch