A library for building AngularJS apps with broken APIs that are delivered late.
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HackStack Build status

What is HackStack?

HackStack is an Angular module that helps you work with backend APIs that are incomplete or altogether missing.

In our experience working on numerous Angular projects, broken or delayed backend APIs are quite common and can present a major risk if the front end team cannot find a good way to react in this situation. After trying a number of approaches, we've found client-side mocking to the be most effective route.

We've done it a few different ways on a number of projects and presented some of our observations in a talk at ngConf in 2015. We've got a lot of positive response, but also a question: "Why don't you make this a reusable library?" So we did. Enter HackStack.js, the library.

Installing with Bower

The easiest way to install HackStack is by using bower:

  bower install --save angular-hackstack

Alternatively, build HackStack using this repo.

Using HackStack

To create a new HackStack endpoint, call:

  var mockEndpoint = hackstack.mock(data);

This creates a fully mocked endpoint which won't make any calls to the backend at all. Here, data can be either an array of items or a path to a json file.

Alternatively, you can "wrap" an existing endpoint: HackStack will then get the data from the server and fill in the missing properties of each item based on a provided template object:

  var wrappedEndpoint = hackstack.wrap(endpoint, templateObject);


  var mockEndpoint = hackstack.mock([
      'name': 'Alice',
      'id': 1
      'name': 'Bob',
      'id': 2

    .then(function (response) {
      console.log(response.data); // logs {'name': 'Alice', 'id': 1}

A full example is available under the example directory

Controlling HackStack from the Browser Console

While you're working with HackStack, you may want to force a particular error to happen on the next call to the endpoint. You can do this by exposing the mock endpoint object to the console and then calling .forceError(<HTTP ERROR CODE>) on it. Subsequent requests will then return that error. Call .forceError(null) to turn this off.

Random Errors

HackStack defaults to generating random errors in response to endpoint requests. You can turn this off using .disableError(true) on your mock endpoint object. You can turn it back on by calling the same method with false.

Artificial Delay

HackStack introduces randomized artificial delay on all requests. This helps you detect cases where your code makes optimistic assumptions about timing.


This library currently makes a couple of assumptions:

  • You're using AngularJS. It's designed using AngularJS services.

  • You're using an abstraction factory to wrap your end points. This service will provide you an object that has methods for getting all records, getting a single record, creating a record, etc.



This service provides methods that are used by both hackstack.mock and hackstack.wrap services. Those functions are:

  • addErrorTrigger(errorFn, errorCode, method): Adds an "error trigger" that will fire if errorFn(response) returns true (where response is the response object that would otherwise be returned by HackStack)
    errorFn : {function} predicate that decides whether error should be returned
    errorCode : {integer} HTTP error code to return
    method : {string} Which HTTP method to check error trigger against (e.g. 'POST')
  • disableRandomErrors(value): Disable random error generation.
    value : {boolean}
  • forceError(errorCode): Reject with this error code in the next response. Reset error if errorCode is null
    errorCode : {integer}
  • produceError(errorArray): Return either an error object or null depending on the probability distribution defined in the errorArray
    errorArray : {[object]} (optional) an array of error objects
  • randomError(errorArray): Return a random error from an array of errors (errorArray or the default error array if none provided)
    errorArray : {[object]} (optional) an array of error objects
  • getErrorByCode(errorCode): Returns an error object with error code matching errorCode.
    errorCode : {integer}
  • randomInt(): Returns a random integer.
  • setOptions(newOptions): Updates the HackStack options list
    newOptions : {object}
  • waitForTime(): Returns a promise that resolves after some time. Used to mimic latency


hackstack.mock is a service that creates a mock backend from scratch. To create a HackStack instance, call hackstack.mock(mockData, options) where mockData is an array of objects and options is an optional argument of type Object.

Alternatively, mockData can be the path to a JSON that is an array of objects

A hackstack.mock object contains the following methods:

  • getAll(): Get all results (equivalent to requesting API_BASE/endpoint/)
  • get(id): Get a single result (equivalent to requesting API_BASE/endpoint/id)
  • query(queryObject): get the first result where for any key:value pair in queryObject, there's a matching key:value pair in the mock data object
    queryObject : {object}
  • create(object, createIdFn): Create a new record
    object : {object}
    createIdFn : {() -> int} Function that returns an integer to be used as an id
  • update(id, object): Update a record.
    id : the id of the record
    object : {object} the object to update
  • save(object, createIdFn): a method that will call create or update depending on presence of an id.
    signature is identical to create


hackstack.wrap is a service that wraps a real backend with a local mock object. It can be useful if the backend is buggy, returns incomplete data, or is yet to be fully implemented.

To create a hackstack.wrap instance, call hackstack.wrap(endpoint, mockObject, options) where:

  • endpoint is a string that contains the location of the endpoint
  • mockObject is a single object used to complete responses from the backend
  • options is a an object (optional argument)

Note that unlike hackstack.mock, you only pass a single object to hackstack.wrap. It will use that one object to complete all of the responses your backend returns by deep merging the response's properties with the objects

hackstack.wrap also requires that you make API_BASE available through Angular's injector. API_BASE should be a string that contains the base URL for your API.

the hackstack.wrap factory returns an object which contains the same methods as a hackstack.mock object. Keep in mind however, that hackstack.wrap will relay all requests to the backend, including post requests.