cf-errors

Extensible error library.

##Installation

$ npm install cf-errors

• Creating an error
• Extending with a previous error
• Printing the stack
• toString
• Predefined errors
• Inheriting the previous error type
• Getting the value of the first occurrence of a field in the chain
• Running the tests

##Creating an error

var CFError = require('cf-errors');
var error   = new CFError("error message");

###Extending the error

var error = new CFError({field: "value", message: `error message`});

###Setting the error name

var error = new CFError({name: "ErrorType", message: "my error name"});

###Passing multiple objects will extend the previous objects

var error = new CFError({field: "value", message: `error message`}, {field2: "value"}, {field: "override first value"});

###Last argument passed to the constructor can be a string, which will populate the message field automatically

var error = new CFError({field: "value", message: `error message`}, {field2: "value"}, "my error message");

##Extending with a previous error

var extendedError = new CFError({
    message: `extended error message`,
    cause: error
});

##Printing the stack will print the stack of all previous errors too

console.log(extendedError.stack);

##toString() Will print the whole chain of errors in a nice way. You can always override it if you want.

CFError.prototype.toString = function(){
    //your implementation
}

##Predefined Error Types

var CFError    = require('cf-errors');
var Errors     = CFError.Errors;

All predefined errors are exposed on 'CFError.Errors' object. They are actually just simple objects so using the extension capability allows us to use them easily and extend them when needed. ####Http Errors All http errors are available. They will contain a field name 'statusCode' for your use.

var error = new CFError(Errors.Http.BadRequest, {
    message: `failed to validate your request`
});

If you are using express.js then your error middleware can look something like this:

app.use(function(err, request, response, next){
    console.error(err.stack);
    var statusCode = 400;
    if (err.constructor && err.constructor.name === "CFError") {
        statusCode = err.statusCode || statusCode;
    }
    return response.status(statusCode).send(err.message);
});

####Node Errors All node.js core errors are also available using the Errors.Node object.

##Inheriting the previous error type Creating an error with the same name as its cause can be achieved using 'Inherit' as the error name.

var extendedError = new CFError(Errors.Inherit, {
    message: `extended error message`,
    cause: error
});

This will also work

var extendedError = new CFError({
    name: "Inherit",
    message: `extended error message`,
    cause: error
});

##Getting the value of the first occurrence of a field in the chain Sometimes you will populate an error with a field and wrap it with an additional error. In order to get the value of the field you will need to recursively go over the whole chain. In order to get the first value of a field in the chain use 'getFirstValue' function.

var error = new CFError({field: "value", field1: "firstValue"});
var extendedError = new CFError({cause: error, field1: "newValue"});
extendedError.getFirstValue('field') // "value"
extendedError.getFirstValue('field1') // "newValue"
extendedError.getFirstValue('field2') // undefined

##Running the tests 'npm test' or 'gulp unit_test'