JavaScript RangeError: Invalid array length

A plain-words explanation of this JavaScript message: what it means, the usual causes, and the steps that fix it.

The messageUncaught RangeError: Invalid array length

Make the error yourself

Run in Google Chrome 157.0.8103.51. This is the smallest example we could find that shows it.

JavaScript (in a script tag)

const size = -1;
const list = new Array(size);
console.log(list);

Browser console (the real message)

RangeError: Invalid array length

Why it happens

An array length must be a whole number from 0 to 4,294,967,295. new Array(-1), a decimal such as new Array(2.5) or setting list.length = -1 is outside that range, so the engine raises a RangeError. In real programs the number usually comes from a calculation that went wrong, such as a count minus something, a value that is NaN, or an input that was never validated.

How to fix it

1. Log the number that you pass in.
2. Check it before use: Number.isInteger(n) && n >= 0.
3. Use Math.max(0, n) when a small negative result should mean "none".
4. For lists you build, use [] and push instead of choosing a length first.

The corrected version

JavaScript (in a script tag)

const size = Math.max(0, -1);
const list = new Array(size);
console.log(list.length);

Browser console (the corrected version)

0

How to avoid it

Validate numbers from input and from calculations before using them as sizes or counts.

Questions

This is an independent guide. It is not connected with Python, Microsoft, Google, GitHub or the Git project. Product names belong to their owners. Examples were run on 13 November 2026 in a practice folder or a blank workbook; your version may word a message slightly differently.