ono (Oh No!)

Throw better errors.

Features

• Wrap and re-throw an error without losing the original error's type, message, stack trace, and properties

• Add custom properties to errors — great for error numbers, status codes, etc.

• Use format strings for error messages — great for localization

• Enhanced support for JSON.stringify() and util.inspect() — great for logging

• Supports and enhances your own custom error classes

• Tested on Node.js and all modern web browsers on Mac, Windows, and Linux.

Example

const ono = require("@jsdevtools/ono");

// Throw an error with custom properties
throw ono({ code: "NOT_FOUND", status: 404 }, `Resource not found: ${url}`);

// Wrap an error without losing the original error's stack and props
throw ono(originalError, "An error occurred while saving your changes");

// Wrap an error and add custom properties
throw ono(originalError, { code: 404, status: "NOT_FOUND" });

// Wrap an error, add custom properties, and change the error message
throw ono(originalError, { code: 404, status: "NOT_FOUND" }, `Resource not found: ${url}`);

// Throw a specific Error subtype instead
// (works with any of the above signatures)
throw ono.range(...);                           // RangeError
throw ono.syntax(...);                          // SyntaxError
throw ono.reference(...);                       // ReferenceError

// Create an Ono method for your own custom error class
const { Ono } = require("@jsdevtools/ono");
class MyErrorClass extends Error {}
ono.myError = new Ono(MyErrorClass);

// And use it just like any other Ono method
throw ono.myError(...);                         // MyErrorClass

Installation

Install using npm:

npm install @jsdevtools/ono

Usage

When using Ono in Node.js apps, you'll probably want to use CommonJS syntax:

const ono = require("@jsdevtools/ono");

When using a transpiler such as Babel or TypeScript, or a bundler such as Webpack or Rollup, you can use ECMAScript modules syntax instead:

import ono from "@jsdevtools/ono";

Browser support

Ono supports recent versions of every major web browser. Older browsers may require Babel and/or polyfills.

To use Ono in a browser, you'll need to use a bundling tool such as Webpack, Rollup, Parcel, or Browserify. Some bundlers may require a bit of configuration, such as setting browser: true in rollup-plugin-resolve.

API

ono([originalError], [props], [message, ...])

Creates an Error object with the given properties.

• originalError - (optional) The original error that occurred, if any. This error's message, stack trace, and properties will be copied to the new error. If this error's type is one of the known error types, then the new error will be of the same type.

• props - (optional) An object whose properties will be copied to the new error. Properties can be anything, including objects and functions.

• message - (optional) The error message string. If it contains placeholders, then pass each placeholder's value as an additional parameter. See the format option for more info.

Specific error types

The default ono() function may return an instance of the base Error class, or it may return a more specific sub-class, based on the type of the originalError argument. If you want to explicitly create a specific type of error, then you can use any of the following methods:

The method signatures and arguments are exactly the same as the default ono() function.

|Method | Return Type |:---------------------------|:------------------- |ono.error() |Error |ono.eval() |EvalError |ono.range() |RangeError |ono.reference() |ReferenceError |ono.syntax() |SyntaxError |ono.type() |TypeError |ono.uri() |URIError |ono.yourCustomErrorHere() |Add your own custom error classes to ono

Ono(Error, [options])

The Ono constructor is used to create your own custom ono methods for custom error types, or to change the default behavior of the built-in methods.

Warning: Be sure not to confuse ono (lowercase) and Ono (capitalized). The latter one is a class.

• Error - The Error sub-class that this Ono method will create instances of

• options - (optional) An options object, which customizes the behavior of the Ono method

Options

The Ono constructor takes an optional options object as a second parameter. The object can have the following properties, all of which are optional:

|Option |Type |Default |Description |-----------------|------------|-------------|--------------------------------------------------------------- |concatMessages |boolean |true |When Ono is used to wrap an error, this setting determines whether the inner error's message is appended to the new error message. |format |function or boolean |util.format() in Node.js<br><br>false in web browsers|A function that replaces placeholders like in error messages with values.<br><br>If set to false, then error messages will be treated as literals and no placeholder replacement will occur.

concatMessages Option

When wrapping an error, Ono's default behavior is to append the error's message to your message, with a newline between them. For example:

const ono = require("@jsdevtools/ono");

function createArray(length) {
  try {
    return new Array(length);
  }
  catch (error) {
    // Wrap and re-throw the error
    throw ono(error, "Sorry, I was unable to create the array.");
  }
}

// Try to create an array with a negative length
createArray(-5);

The above code produces the following error message:

Sorry, I was unable to create the array.
Invalid array length;

If you'd rather not include the original message, then you can set the concatMessages option to false. For example:

const { ono, Ono } = require("@jsdevtools/ono");

// Override the default behavior for the RangeError
ono.range = new Ono(RangeError, { concatMessages: false });

function createArray(length) {
  try {
    return new Array(length);
  }
  catch (error) {
    // Wrap and re-throw the error
    throw ono(error, "Sorry, I was unable to create the array.");
  }
}

// Try to create an array with a negative length
createArray(-5);

Now the error only includes your message, not the original error message.

Sorry, I was unable to create the array.

format option

The format option let you set a format function, which replaces placeholders in error messages with values.

When running in Node.js, Ono uses the util.format() function by default, which lets you use placeholders such as %s, %d, and %j. You can provide the values for these placeholders when calling any Ono method:

throw ono("%s is invalid. Must be at least %d characters.", username, minLength);

Of course, the above example could be accomplished using ES6 template literals instead of format strings: