EC
ERR_INVALID_ARG_TYPE
Node.jsERRORNotableAPI UsageHIGH confidence

An invalid argument type was provided to a function.

Production Risk

High. This error often points to untested code paths or faulty logic that can cause application crashes. It indicates a clear programming mistake.

What this means

This error occurs when a function or method receives an argument of a different data type than it is designed to accept. For example, providing a number where a string is expected will trigger this error. It signals a fundamental mismatch in the contract between the calling code and the function.

Why it happens
  1. 1A function was called with an incorrect data type for one of its parameters.
  2. 2A variable was unexpectedly reassigned to a different type before being used in a function call.
  3. 3Data from an external source, such as a file or API response, was not validated or parsed correctly before use.
How to reproduce

This error is thrown during function execution when Node.js performs internal type checking on arguments for its core APIs.

trigger — this will error
trigger — this will error
const fs = require('fs');
// The first argument 'path' must be a string, buffer, or URL.
fs.readFile(123, 'utf8', (err, data) => {
  if (err) {
    console.error(err);
  }
});

expected output

TypeError [ERR_INVALID_ARG_TYPE]: The 'path' argument must be of type string or an instance of Buffer or URL. Received type number (123)

Fix 1

Correct the Argument Type

WHEN The data type of an argument passed to a function is incorrect.

Correct the Argument Type
const fs = require('fs');
// Pass a valid file path as a string.
fs.readFile('./my-file.txt', 'utf8', (err, data) => {
  if (err) {
    console.error(err);
  }
});

Why this works

Ensure that all arguments passed to Node.js APIs and other functions match the data types specified in their documentation. Implement type validation in your own functions to provide clear errors.

Fix 2

Validate External Input

WHEN Data is sourced from external inputs like user forms, API responses, or files.

Validate External Input
function readFileFromInput(userInput) {
  if (typeof userInput.filePath !== 'string') {
    throw new TypeError('The provided file path must be a string.');
  }
  // ... proceed to read file
}

Why this works

Before using data from external sources, always validate its type and structure to ensure it conforms to the expected format.

Code examples
Triggerjs
const fs = require('fs');
// The first argument 'path' must be a string, buffer, or URL.
fs.readFile(123, 'utf8', (err, data) => {
  if (err) {
    console.error(err);
  }  // this triggers ERR_INVALID_ARG_TYPE
Handle in try/catchjs
try {
  // operation that may throw ERR_INVALID_ARG_TYPE
  riskyOperation()
} catch (err) {
  if (err.code === 'ERR_INVALID_ARG_TYPE') {
    console.error('ERR_INVALID_ARG_TYPE:', err.message)
  } else {
    throw err
  }
}
Defensive pattern to avoid itjs
function readFileTypeSafe(path, enc, cb) {
  if (typeof path !== 'string') throw new TypeError(`path must be string, got ${typeof path}`)
  require('fs').readFile(path, enc, cb)
}
What not to do

✕

✕

Sources
Official documentation ↗

https://github.com/nodejs/node/blob/main/lib/internal/errors.js

More information ↗

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