Todd Wolfson

Software Engineer

November 17, 2012

Warning: This article is more opinionated than other ones.

As with everyone, I have began to develop opinions on certain styles of code; some concious and practical, others gutteral and more difficult to explain.

Below is a list of those that fall into the latter category but I have squeezed logic out of.

As a reminder, anti-patterns are not things that should be avoided at all costs; they have their place in quick and simple code. However, for maintainable and future-proof reasons, it is better to avoid them.

Anti-pattern #1: Writing directly to an object

The pattern

var algorithms = {};
algorithms['top-down'] = topDownFn;
algorithms['left-right'] = leftRightFn;
algorithms['diagonal'] = diagFn;

Why this is bad

You have written a direct reference to the map. However, what if you want to move to an array store or the variable becomes abstracted into a class. In either of those cases, those last 3 lines will have to be updated.

If that does not seem like a lot, imagine those were 20 lines and you wound up going back and forth a lot. There is a large margin for error and debugging will also not be fun.

How to make it better

Your first thought is probably "objectify them into an array and iterate over that array". This is not bad for a first thought but as you will see in #2, it still does not fully hit the mark.

It is best to abstract this into a helper function

var algorithms = {};
function addAlgorithm(name, fn) {
  algorithms[name] = fn;
}
addAlgorithm('top-down', topDownFn);
addAlgorithm('left-right', leftRightFn);
addAlgorithm('diagonal', diagFn);

Now we have taken a direct connection and loosened it up a bit.

We can even go one step further and turn this into a full-fledged class.

function AlgorithmKeeper() {
  this.algorithms = {};
}
AlgorithmKeeper.prototype = {
  'add': function (name, fn) {
    var algorithms = this.algorithms;
    algorithms[name] = fn;
  }
};

Bonus

Now that we are going through a function, we can add additional one-off logic, effectively leaving the base function. This is great if the items you are adding are from a repo that you don't own.

function addAlgorithm(params) {
  var name = params.name,
      algorithm = params.algorithm,
      defaults = params.defaults || {},
      saveFn = algorithm;

  // If defaults exist, override the saveFn to fallback to defaults
  if (defaults) {
    saveFn = function (data) {
      _.defaults(data, defaults);
      return algorithm(data);
    };
  }

  // Save our saveFn
  algorithms[name] = saveFn;
}

Anti-pattern #2: Binding by iterating over an array

The pattern

var bindingElts = [{
      'name': 'top-down',
      'fn': topDownFn
    }, {
      'name': 'left-right',
      'fn': leftRightFn
    }, {
      'name': 'diagonal',
      'fn': diagFn
    }];
bindingElts.forEach(function (bindingElt) {
  addAlgorithm(bindingElt.name, bindingElt.fn);
});

Why this is bad

It is harder to distinguish items and account for one-off cases. Additionally, if there is an issue inside of the forEach itself, the stack trace will not inform you which item failed. The stack trace will provide the line number of addAlgorithm but nothing about the specific bindingElt.

How to make it better

addAlgorithm('top-down', topDownFn);
addAlgorithm('left-right', leftRightFn);
addAlgorithm('diagonal', diagFn);

This makes each item have a nice line number attached to the stack trace which will lead to faster debugging.

Bonus

If there is a problem we need to debug, we can take the trouble-maker line and pass it through a one-off function. This effectively isolates it from the noise of other bindings.

function addAlgorithmDebug(name, fn) {
  console.log('Adding ' + name + ' to algorithms');
  algorithms[name] = fn;
  console.log('Done adding ' + name + ' to algorithms');
}
addAlgorithm('top-down', topDownFn);
addAlgorithmDebug('left-right', leftRightFn);
addAlgorithm('diagonal', diagFn);

Anti-pattern #3: Defining a finite set of similar types

The pattern

var algorithms = {
      'top-down' : topDownFn,
      'left-right': leftRightFn,
      'diagonal' : diagFn
    };

Why this is bad

This one isn't that bad but it can be improved. This pattern unintentionally limits others from adding new items to the set. Another side effect is that there is no easy way to hook into when an addition occurs.

How to make it better

As we have demonstrated in #1, we can use a function like addAlgorithm. Then, we can expose addAlgorithm to make setting up another one easily for others.

var algorithms = {};
function addAlgorithm(name, fn) {
  algorithms[name] = fn;
}
addAlgorithm('top-down', topDownFn);
addAlgorithm('left-right', leftRightFn);
addAlgorithm('diagonal', diagFn);

module.exports = {
  'algorithms': algorithms,
  'addAlgorithm': addAlgorithm
};

Bonus

What you might not notice at first glance is that addAlgorithm is the Observer pattern.

AlgorithmKeeper.on('add', function (name, fn) {
  algorithms[name] = fn;
});
AlgorithmKeeper.emit('add', 'top-down', topDownFn);
AlgorithmKeeper.emit('add', 'left-right', leftRightFn);
AlgorithmKeeper.emit('add', 'diagonal', diagFn);

In previous examples, we have simplified it by removing the need for a third party tracker.

However, if we did go this route, then we could have other people listen and hook in to our algorithm addition events. CRAZY AWESOME!!

AlgorithmKeeper.on('add', function (name) {
  console.log('Someone is adding a new algorithm: ' + name);
});

Anti-pattern #4: Composition of functions

The pattern

function addSalt(str) {
  return str + 'salt';
}
function addPepper(str) {
  return str + 'pepper';
}

var pasta = 'pasta';
pasta = addSalt(addPepper(pasta));

Why this is bad

The code is not quickly and easily readible. However, the issue arises out of adding new items

function addSauce(str) {
  return str + 'sauce';
}
function addRosemary(str) {
  return str + 'rosemary';
}

var pasta = 'pasta';
pasta = addSalt(addPepper(addSauce(addRosemary(pasta))));

Ah, that is nice and Lispy now. We could add line feeds or break it into separate lines but that is lipstick on a pig.

The worst would be to add all 4 functions into a single function. Then, all functional combinations would reach 15 functions addSaltAndPepper, addSaltAndSauce, …, addSaltPepperSauceRosemary (excluding noop). Clearly, that is not maintainable.

How to make it better

If we step back, we can notice that we are constantly passing the same state into each function. Classes were built for this; functions are stateless and classes are stateful.

If we move this into a class with a fluent interface, life becomes awesome.

function Food(str) {
  this.str = str;
}
Food.prototype = {
  'addSalt': function () {
    this.str += 'salt';
    return this;
  },
  'addPepper': function () {
    this.str += 'pepper';
    return this;
  },
  'addSauce': function () {
    this.str += 'sauce';
    return this;
  },
  'addRosemary': function () {
    this.str += 'rosemary';
    return this;
  }
};
var pasta = new Food('pasta');
pasta.addSalt().addPepper().addSauce().addRosemary();

Side note: If you have been paying attention, you might notice the prototype is a finite set. I usually let prototypes slide by this rule. However, we could consider adding a method like addCondiment which would add a new method onto the prototype.

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