Get Error

Safely parse anything into an Error instance

Getting Started

npm install get-error

Example Usage

import { getError } from "get-error";

try {
  await Promise.reject({ message: "Something went wrong" });
} catch (err) {
  const error = getError(err); // Guaranteed to get an Error instance
  console.error(error.message); // Safely access `.message` property
}

That's it!

Motivation

In JavaScript, even though there is a strong convention to always throw Error instances, it's not mandatory. Technically, any value can be thrown:

try {
  throw "Something went wrong";
} catch (error) {
  console.log(typeof error); // string
}

Throwing Responses

While throwing strings is unlikely, it's quite popular to come across APIs that throw error-like objects or Response objects:

try {
  throw new Response("Unauthorized", { status: 401 });
} catch (error) {
  console.log(getError(error).message); // 401
}

This is a common practice in Remix

JSON-RPC Error Objects

Another popular case is JSON-RPC APIs: https://www.jsonrpc.org/specification#error_object

try {
  throw {
    id: 1,
    jsonrpc: "2.0",
    error: {
      code: -32601,
      message: "Method not found",
      data: null,
    },
  };
} catch (unknownError) {
  // You'd have to do something like `error.error.message`
  const error = getError(unknownError); // returns Error instance and preserves `code` and `data` fields
  console.log(error.message); // "Method not found"
}

Handy in building User Interaces

import React from "react";
import { useQuery } from "@tanstack/react-query";

function App() {
  const { data, isError, error } = useQuery({
    queryKey: ["data"],
    queryFn: async () => {
      return Promise.reject(new Response(null, { status: 404 }));
    },
  });

  if (isError) {
    // return <p>{error.message}</p> // ❌ NOT safe!
    return <p>{getError(error).message}</p>; // ✅ Safe!
  }
  return <div>{data}</div>;
}