Input Resolver

Resolver is helper object used for checking input data.

Installation

npm install input-resolver --save-dev

Instantiation

To start using Resolver you have to instantiate it. Its module exports Resolver constructor, not an object.

var resolver = new (require('input-resolver'))();     // one-line instantiation

var resolverConstructor = require('input-resolver'); // instantiation via
var resolver = new resolverConstructor();        // construction function

Add parameters

For parameters addition use addParameter(<parameter>) function. <parameter> object passed to addParameter() function can accept properties:

• name (required)
• required (required)
• type
• default
• values
• parent

type property can be string, number, boolean, array or object. For optional parameters (required is false) default value can be set, but be cautious: if you set type property for this parameter and default value's type doesn't match it Resolver will throw an error:

/*
    Throws: "Resolver error: default value doesn't match the param type" 
*/
resolver
    .addParameter({ 
        name: 'isActive',
        required: false,
        type: boolean,
        default: 'true'
    })
;

Also attempting to attach default value to required parameter lead to an error:

/* Throws: "Resolver error: trying to set default value to required parameter" */
resolver.addParameter({ name: 'isActive', required: true, default: 'true' });

values property is an array of available values for parameter.

addParameter() returns Resolver object so it is chainable:

resolver
    .addParameter({ name: 'username', required: true })
    .addParameter({ name: 'email', required: true })
    .addParameter({ name: 'description', required: false })
;

parent property defines container object for given parameter. Its existence will be checked not inside the input data, but inside its suboject named parent. If parent parameter was not defined it would be created. Only 1 level of hierarchy is allowed for now (you cannot define parent for parent). If it was defined with type different from object resolver would throw an error:

/*
    Throws: "'Resolver error: parent for parameter "isActive" is defined,
    but has type of "number" instead of "object"'" 
*/
resolver
    .addParameter({ name: 'parent', required: true, type: 'number' })
    .addParameter({ name: 'isActive', required: true, parent: 'parent' })
;

This property can be useful to define additional (parent parameter) check implicitly.

Check input data

To check input data resolve() method is used:

resolver
    .addParameter({ name: 'username', required: true })
    .addParameter({ name: 'email', required: true })
;

var resolved = resolver.resolve(
    {
        username: 'Ivan',
        email: '[email protected]'
    }, 
    
    function(err, data) {
        console.log(data);    
    }
);

// output: { username: 'Ivan', email: '[email protected]' }

Input object's properties that were not specified would be ignored:

resolver
    .addParameter({ name: 'username', required: true })
;

var resolved = resolver.resolve({
    username: 'Ivan',
    email: '[email protected]',
    description: 'This message will never be displayed'
}, function(err, data) {
    console.log(data);
});
// output: { username: 'Ivan' }

If required parameter is missing or parameter has wrong value or type the different type of Error will be returned. This feature will help you to distinguish different error types.

Putting it all together

var resolver = new (require('input-resolver'))();

resolver
    .addParameter({ name: 'username', required: true })
    .addParameter({ name: 'email', required: true })
    .addParameter({ name: 'isActive', required: false, type: 'boolean' })
    .addParameter({ name: 'description', required: false, default: 'Default description' })
;

resolver.resolve(inputData, function(err, data) {
    if (err) {
        if ('NO_REQUIRED_PARAMETER' == err.name) {
            console.log('Some of the required parameter are not specified');
        } else if ('PARAMETER_WRONG_TYPE' == err.name) {
            console.log('"isActive" parameter has wrong type');
        }    
    } else {
        console.log('Data successfully validated');
    }
});

Promises

Since v1.2.0 Input Resolver can return Promise object:

resolver
    .addParameter({ name: 'username', required: true })
;

var promise = resolver.resolvePromise(someData);

promise
    .then(
        function(dataResolved) { /* validated data */ }, 
        function(err) { /* validation error */ }
    )
;