Erray

Define an array of errors in JavaScript based on a specification.

Overview

Easily be able to detect types of error messages by defining an error specification, and then using instanceof and/or code to determine the type of error and handle errors appropriately.

Known Issues

Extending 'Error' is not trivial as lineNumber, columnNumber and fileName in addition to stack properties are vendor specific. For example within Mozilla Firefox, the lineNumber property will reference the incorrect line, and will point to a line inside of the class rather then where the error was thrown. Currently lineNumber, columnNumber and fileName are not accessible from Firefox. Please see Error - JavaScript | MDN for more information.

Handling an Error

// detect the error type with instanceof
if (e instanceof Errors.InvalidY) {
   ...
}

// detect the error type with error code
if (e.code === 500) {
   ...
}

Installing

Works in both web browsers and in Node.js

<script type="text/javascript" src="dist/erray.min.js"></script>
<script>
  var Erray = window.erray;
</script>

npm install erray --save

var Erray = require('erray');

Defining Errors

Errors are defined with a concise specification.

var Errors = Erray([
  'InvalidX', // basic usage, only specify a name
  {
    name: 'InvalidY', // specify the name
    message: 'Invalid Y value for this function', // set a default static message
    code: 500 // add an optional code
  },
  {
    name: 'InvalidXY',
    message: function(x, y) { // specify a function to handle arguments
      return 'Invalid values x: ' + x + ' and y: ' + y + ' for input.'; 
    }
  },
  {
    name: 'NotFound',
    code: 404
  }
]);

Errors can then be thrown or returned by instantiating a new error:

var error = new Errors.NotFound('The requested information is not found');

Message Formatting

Error messages can be generated by passing a function in the specification that will handle arguments when the error is instantiated.

var x = 10;
var y = 23;
var error = new Errors.InvalidXY(x,y);
throw error;

// Example Log
//
// InvalidXY: Invalid values x: 10 and y: 23 for input.
//    at repl:1:7
//    at REPLServer.self.eval (repl.js:110:21)
//    at repl.js:249:20
//    at REPLServer.self.eval (repl.js:122:7)
//    at Interface.<anonymous> (repl.js:239:12)
//    at Interface.EventEmitter.emit (events.js:95:17)
//    at Interface._onLine (readline.js:202:10)
//    at Interface._line (readline.js:531:8)
//    at Interface._ttyWrite (readline.js:760:14)
//    at ReadStream.onkeypress (readline.js:99:10)

The specification can also include a default message, or send it directly when instantiating.

// use the default message
var error = new Errors.InvalidY();

// or you can supply a message directly 
var error = new Errors.InvalidY('The value of y: "' + y + '" is invalid.');