JavaScript

ERR_INVALID_ARG_TYPE: What It Means and How to Fix It

Error reference

ERR_INVALID_ARG_TYPE

Language

JavaScript

Severity

Medium

When it happens

Node.js throws ERR_INVALID_ARG_TYPE when a built-in API function receives an argument of the wrong type.

Potential fixes

Read the error message carefully: it names the argument and the expected type. Validate input types before passing them to Node.js APIs. Use TypeScript or JSDoc types to catch these mismatches at development time.

Deep dive

Node.js throws ERR_INVALID_ARG_TYPE when a built-in API function receives an argument of the wrong type. The error message specifies the argument name, the expected type(s), and the actual value received.

Why it happens

•Passing a number where a file path string is expected.
•Passing undefined or null to a function that requires a Buffer or string.
•A variable holding the wrong type due to an earlier logic error.
•Destructuring the wrong property from an object before passing it to an API.

Potential fixes

Read the error message carefully: it names the argument and the expected type. Validate input types before passing them to Node.js APIs. Use TypeScript or JSDoc types to catch these mismatches at development time.

Examples

JavaScript

Code that triggers the error

const fs = require("fs");
fs.readFile(123, "utf8", (err, data) => console.log(data));

Error 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)

Fixed code

const fs = require("fs");
fs.readFile("./data.txt", "utf8", (err, data) => {
  if (err) throw err;
  console.log(data);
});

Practice in English

How would you explain an ERR_INVALID_ARG_TYPE to a fellow dev? Choose the right phrase:

"I hit an error...

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