Safetify

Safetify is a tool for resolving received data from 3rd party applications (eg. API) to make data strongly-typed. Thanks to that we don't need to take care later on about unexpected undefined values or value type.

Installation

To install Safetify simply use npm:

npm install safetify --save

Introduction

Received from 3rd party applications data are never strongly-typed so we can get any value in place we expect specifically typed one. Not always something that fits data we made application for. As example we can take bug in API because of which we wouldn't receive specific value or even get empty result. We need to prevent of situations like that one simply by checking for nulls, undefined values or by mapping data to validated model.

Say we would receive from API data like this:

{
    "name": "John Doe",
    "age": 30,
    "isSingle": false
}

With Safetify we can resolve the data in that way:

import * as Safetify from 'safetify';

let personResolver: Safetify.Object = Safetify.Object<IPerson>({
    name: Safetify.String(),
    age: Safetify.Number(),
    isSingle: Safetify.Boolean()
});

let person: IPerson = personResolver.resolve(data).result;

Or use alternative imports:

import { ObjectResolver, StringResolver, NumberResolver, BooleanResolver } from 'safetify';

let personResolver: ObjectResolver = ObjectResolver<IPerson>({
    name: StringResolver(),
    age: NumberResolver(),
    isSingle: BooleanResolver()
});

let person: IPerson = personResolver.resolve(data).result;

And then data will always be the exact type no matter if we received correct data or not. It prevents of many cases of using methods dedicated to specific types of data. Say we got undefined value in name property and now we want to use toUpperCase method on that data. Basically it would look like that:

let name = person.name; // it's undefined

name.toUpperCase();

This would throw us a TypeError exception. Safetify in that case will convert failed data to empty string so in result we will always be operating on string:

let name = person.name; // now it's empty string

name.toUpperCase();

This won't throw any exception of course.

Usage

Safetify works both with TypeScript and JavaScript. Look on unit tests or documentation to get more familiar with.

Primitive types have no arguments to pass, ie. we can use resolvers:

• StringResolver
• NumberResolver
• BooleanResolver

just like StringResolver().resolve(<anyString>).

In case of advanced types like object we need to pass structure or values (as we did it in example above).

Additional functionality is a possibility to set nullable and default value (default is available only for primitives and enum).

let personResolver: ObjectResolver = ObjectResolver<IPerson>({
    name: StringResolver().defaultsTo('Johnny'),
    age: NumberResolver(),
    isSingle: BooleanResolver().nullable()
});

After resolving any type of data resolve method will always return Result object which has 3 properties:

• success as boolean,
• result as resolved data type,
• error if success is false as string[].

If resolving was not succeeded then error property will always describe what went wrong (and which property in if resolved data was object or array)

Resolvers list

Safetify provides resolvers for couple of data types:

• AnyResolver - just returns what it gets on input
• NumberResolver - resolves number values
• StringResolver - resolves string values
• BooleanResolver - resolves boolean values
• ArrayResolver - resolves arrays
• ObjectResolver - resolves object with specific structure (eg. model)
• DictionaryResolver - resolves object which is a dictionary (has n key-value pairs of specific type)
• PartialResolver - resolvers object which is subset of another object with specific structure (eg. model)
• EnumResolver - resolves enum (if input is correct value of given enum)
• DateResolver - resolves dates. This includes Date object, string-date and timestamp
• TupleResolver - resolves tuple of given structure
• OneOfResolver - resolves input which can be one of given type

For examples and more, look on documentation.

Constraints

Constraints are simple functions to check resolved value under specified condition. Say we want to get only positive numbers. We can make constraint like this:

const positiveResolver: NumberResolver = NumberResolver().constraint((n: number) => n >= 0);

positiveResolver.resolve(5);

Now if value is not positive, Result will have success as false and error with constraint number.

positiveResolver.resolve(-5);

/*
    Returns:
    {
        success: false,
        result: -5,
        error: [ 'constraint #0 failed' ]
    }
*/

To make it more clear we can set own error in simplest way:

const positiveResolver: NumberResolver = NumberResolver().constraint((n: number) => n >= 0 || 'Value is not positive');

positiveResolver.resolve(-5);

/*
    Returns:
    {
        success: false,
        result: -5,
        error: [ 'Value is not positive' ]
    }
*/

As You saw in examples above, Safetify returns -5 as a result. It's because this is still correct value in terms of type safety. I assume dev would like to get -5 more than NaN value. In case we would like to change value if constraint is failed, default value can be set:

const positiveResolver: NumberResolver = NumberResolver().constraint((n: number) => n >= 0 || 'Value is not positive', 0);

positiveResolver.resolve(-5);

/*
    Returns:
    {
        success: false,
        result: 0,
        error: [ 'Value is not positive' ]
    }
*/

Much better but sometimes it's still not perfect (especially in this example). Say we want to change all values to positive if there is failed constraint and value is negative. Default value argument can take also default value transform function:

const positiveResolver: NumberResolver = NumberResolver().constraint((n: number) => n >= 0 || 'Value is not positive', (n: number) => Math.abs(n));

positiveResolver.resolve(-5);

/*
    Returns:
    {
        success: false,
        result: 5,
        error: [ 'Value is not positive' ]
    }
*/

And that's all the simple stuff of constraints. Btw. they works only on primitive types resolvers.

Utilities

Safetify provides bunch of utilities for checking type of values like isDefAndNotNull(), isObject(), isDateLike() etc. You can use them via Safetify.util property. All functions are described here. Most of the functions are based on Google's Closure Library's Goog functions.

Building

If You want to contribute or fork this library firstly install all dependencies:

npm install

Then You can simply build it with:

npm run build

To run unit tests use:

npm test

To generate documentation use:

npm run jsdoc