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erroz

Descriptive errors through metadata

Build Status

Typical strategies of parsing errors are fragile and couple code to the error messages. By defining error objects consistently, working with errors becomes predictable and efficient.

Features

  • arbitrary error metadata
  • templated error messages
  • stack traces
  • JSend format errors

Example

var erroz = require("erroz");

var DuplicateError = erroz({
    name: "Duplicate",
    code: "duplicate",
    statusCode: 409,
    template: "Resource %resource (%id) already exists"
});

// ...

throw new DuplicateError({ resource: "Unicorn", id: 1 });

/*
 throw new DuplicateError();
 ^
 Duplicate: Resource Unicorn (1) already exists
 at Object.<anonymous> (/erroz/examples/staticErrorMessage.js:14:7)
 at Module._compile (module.js:456:26)
 at Object.Module._extensions..js (module.js:474:10)
 at Module.load (module.js:356:32)
 at Function.Module._load (module.js:312:12)
 at Function.Module.runMain (module.js:497:10)
 at startup (node.js:119:16)
 at node.js:902:3
 */

Installation

npm install --save erroz

Defining errors

var errorDefinition = {
    name: "NotFound",
    template: "%resource (%id) not found"
};

var NotFoundError = erroz(errorDefinition);

errorDefinition object

Arbitrary data structure for metadata which will be available on every error instance. Some attributes have a special meaning which is why they are described below:

name string

The name displayed when the error is thrown.

message string

A static error message.

template string

A dynamic error message. Variable substitution from the data object is done with %<variable name>.

Throwing (with data object)

var data = { resource: "Unicorn", id: 1 };
throw new NotFoundError(data);
// Duplicate: Resource Unicorn (1) already exists

data object

A set of data to be used with the errorDefinition.template property.

Throwing (with error message)

var overrideMessage = "You are not authorized to eat my cookies";
throw new ForbiddenError(overrideMessage);
// Forbidden: You are not authorized to eat my cookies

overrideMessage string

A message to override errorDefinition.message or errorDefinition.template. Use of this option will set error.data to an empty object.

JSON

Errors can be converted to JSON with JSON.stringify().

var err = new DuplicateError({ resource: "Unicorn", id: 1 });
console.log(JSON.stringify(err));

/*
 {
    "name": "Duplicate",
    "code": "duplicate",
    "status": "fail",
    "statusCode": 409,
    "template": "Resource %resource (%id) already exists",
    "data": {
        "resource": "Unicorn",
        "id": 1
    },
    "message": "Resource Unicorn (1) already exists"
 }
 */

Custom JSON format

The AbstractError.toJSON method can be defined to customize the JSON format.

// Set a custom `toJSON` method for all errors
erroz.AbstractError.prototype.toJSON = function() {
    return {
        name: this.name,
        code: this.code
    };
};

console.log(JSON.stringify(err));
/*
 {
    "name": "Duplicate",
    "code": "duplicate"
 }
 */

error.toJSend()

Converts the error to a JSend-style object. The JSend status attribute is derived from the statusCode if not passed explicitly. Valid codes are 4xx and 5xx. In case of an invalid statusCode, .toJSend() will throw an error.

var err = new DuplicateError({ resource: "Unicorn", id: 1, status: 409 });

err.toJSend();

/*
 {
    "status": "fail",
    "code": "duplicate",
    "message": "Resource Unicorn (1) already exists",
    "data": {
    	"resource": "Unicorn",
    	"id": 1,
    	"stack": "Duplicate: Resource Unicorn (1) already exists\n    at Object.<anonymous> (/erroz/examples/				  toJson.js:13:11)\n    at Module._compile (module.js:				  456:26)\n    at Object.Module._extensions..js (module.js:474:10)\n    at Module.load 				  (module.js:356:32)\n    at Function.Module._load (module.js:312:12)\n    at 			     Function.Module.runMain (module.js:497:10)\n    at startup (node.js:119:16)\n    at node.js:				  906:3"
    	}
}
*/

Options

renderMessage function

Define a custom error renderer.

erroz.options.renderMessage = function(data, template) {
    return "Ooops";
}

includeStack boolean

Whether the stack should be included in errors. Default is true.

erroz.options.includeStack = false;

Consider turning this off in production and sending it to a logger instead.

Pro Tip: Using erroz with Connect / Express error handlers

Define a global error handler which calls toJSend() if the error is an instance of erroz.AbstractError. why do this? So you can simply next all your errors in your route-handlers.

function myAwesomeRoute(req, res, next) {
    if (!req.awesome) {
        next(new NotAwesomeError()); 
        return; 
    }

    next();
}	
app.use(function errozHandler(err, req, res, next) {
    if (err instanceof erroz.AbstractError) {
        res.status(err.statusCode).send(err.toJSend()); 
        return; 
    } 

    // Pass on all non-erroz errors
    next(err);
});

Licence

MIT

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Streamlined errors with descriptive error messages through metadata and error codes

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