Home

Awesome

dale

"Don't write that stuff until you've tried to live without it and fully understand why you need it." -- James Hague

dale is a tool for iterating over arrays, objects and other values. Why did I write this instead of using underscore or lodash? Well, because I want a very small library that only contains the looping constructs that I always need, no more.

Small as it is, dale is superior to writing for (var a in b) in the following respects:

  1. It can iterate an input that's neither an array nor an object - this input is interpreted as being an array with one element - except that when it is undefined, it will be interpreted as an empty array.

    
[1, 2, 3]          // interpreted as [1, 2, 3]

{a: 1, b: 2, c: 3} // interpreted as {a: 1, b: 2, c: 3}

[]                 // interpreted as []

{}                 // interpreted as {}

'hola!'            // interpreted as ['hola!']

3                  // interpreted as [3]

null               // interpreted as [null]

undefined          // interpreted as []

  2. Array iterator variables (the a in for (var a in b) whenever b is an array) are numbers instead of strings, so you don't have to remember to use parseInt to do math with the iterator.

    
var input = ['a', 'b', 'c'];

for (var i in input) {
   console.log ('Element #' + (i + 1) + ' is ' + input [i]);
}

// This loop will print:
//    Element #01 is a
//    Element #11 is b
//    Element #21 is c

dale.go (input, function (v, k) {
   console.log ('Element #' + (k + 1) + ' is ' + v);
});

// This function will print:
//    Element #1 is a
//    Element #2 is b
//    Element #3 is c

    This also is the case for arguments pseudo-arrays:

    var argumentsTest = function (A, B, C) {
   dale.go (arguments, function (v, k) {
      console.log ('Element #' + (k + 1) + ' is ' + v);
   });
}

// The function invocation below will print:
//    Element #1 is a
//    Element #2 is b
//    Element #3 is c

argumentsTest ('a', 'b', 'c');

  3. Provides functions (stop and stopNot) that allow you to exit the loop prematurely if a certain value is returned by an iteration. This allows for code that's more clear as well as more efficient.

    
var input = [1, 2, 'clank', 4];

var output = [];

for (var i in input) {
   if (typeof (input [i]) !== 'number') break;
   else output.push (input [i] * 10);
}

// output will be [10, 20]

output = [];

dale.stop (input, false, function (v, k) {
   if (typeof (v) !== 'number') return false;
   else output.push (v * 10);
});

// output will be [10, 20]

  4. When iterating an object, by default dale will only take into account the keys that are not inherited. This means that when iterating objects you never again have to do a hasOwnProperty check. This default can be overriden by passing an extra argument.

  5. It is functional, so you can invoke dale functions within object literals to generate parts of them in a very compact and elegant way. In other words, loops become expressions instead of statements. This is probably the greatest advantage of them all.

    
var data = {
   key: 'value',
   key2: [1, 2, 3],
   key3: dale.go ([1, 2, 3, 4], function (v) {
      return v * 10;
   })
}

// data.key3 will be equal to [10, 20, 30, 40]

Current status of the project

The current version of dale, v6.0.2, is considered to be stable and complete. Suggestions and patches are welcome. Besides bug fixes or performance improvements, there are no future changes planned.

dale is part of the ustack, a set of libraries to build web applications which aims to be fully understandable by those who use it.

Installation

dale is written in Javascript. You can use it in the browser by sourcing the main file.

<script src="dale.js"></script>

Or you can use this link to the latest version - courtesy of jsDelivr.

<script src="https://cdn.jsdelivr.net/gh/fpereiro/dale@3199cebc19ec639abf242fd8788481b65c7dc3a3/dale.js"></script>

And you also can use it in node.js. To install: npm install dale

dale should work in any version of node.js (tested in v0.8.0 and above). Browser compatibility has been tested in the following browsers:

The author wishes to thank Browserstack for providing tools to test cross-browser compatibility.

<a href="https://www.browserstack.com"><img src="https://bstacksupport.zendesk.com/attachments/token/kkjj6piHDCXiWrYlNXjKbFveo/?name=Logo-01.svg" width="150px" height="33px"></a>

Functions

dale consists of eight functions.

dale.go

dale.go, for vanilla iteration:

The general idea of the function is quite similar to that of Array.map, but the function accepts inputs of any type.


dale.go ([1, 2, 3], function (v) {return v + 1})
// returns [2, 3, 4]

dale.go ({a: 1, b: 2, c: 3}, function (v) {return v + 1})
// returns [2, 3, 4]

dale.go (1, function (v) {return v + 1})
// returns [2]

dale.go ({a: 1, b: 2, c: 3}, function (v, k) {return k + v})
// returns ['a1', 'b2', 'c3']

Notice that dale.go always returns an array with zero or more elements. It will only return an array of zero elements if its input is either an empty object, an empty array, or undefined.


dale.go ([], function (v, k) {return v + 1})
// returns []

dale.go ({}, function (v, k) {return v + 1})
// returns []

dale.go (undefined, function (v, k) {return v + 1})
// returns []

dale.fil

dale.fil, for iteration that filters out some results:


dale.fil ([{id: 1}, {id: 8}, {id: 14}], undefined, function (v) {
   if (v.id < 10) return v;
});
// returns [{id: 1}, {id: 8}]

var members = [
   {name: 'Pepe', active: true},
   {name: 'Dimitri', active: false},
   {name: 'Helmut', active: true}
];

dale.fil (members, undefined, function (v) {
   if (v.active) return {name: v.name};
});
// returns [{name: 'Pepe'}, {name: 'Helmut'}]

Notice that dale.fil always returns an array with zero or more elements.

dale.keys

dale.keys, for returning the keys of an input (almost always an object):

The general idea of this function is quite similar to that of Object.keys, but the function accepts inputs of any type.


dale.keys ({'foo': true, 'bar': false, 'hip': undefined})
// returns ['foo', 'bar', 'hip']

Notice that dale.keys always returns an array with zero or more elements (each of them the keys of the elements within the input).

dale.stop

dale.stop, for stopping the iteration when finding a certain value:

This function, just like dale.stopNot below, has two qualities that distinguish it from the other functions:


var isNumber = function (value) {
   if (typeof (value) === 'number') return true;
   else return false;
}

dale.stop ([2, 3, 4],       false, isNumber)    // returns true
dale.stop ([2, 'trois', 4], false, isNumber)    // returns false
dale.stop ([],              true,  isNumber)    // returns undefined
dale.stop (undefined,       true,  isNumber)    // returns undefined

dale.stopNot

dale.stopNot is the complementary function to dale.stop. The only difference is that it stops when it finds a value that is not equal to the comparison value (which we name stopNot value).


var returnIfNotNumber = function (value) {
   if (typeof (value) === 'number') return true;
   else return value;
}

dale.stopNot ([2, 3, 4],       true, returnIfNotNumber)    // returns true
dale.stopNot ([2, 'trois', 4], true, returnIfNotNumber)    // returns 'trois'
dale.stopNot ([],              true, returnIfNotNumber)    // returns undefined

dale.acc

dale.acc is a function for accumulating results into one and then returning it. This function:

The general idea of this function is quite similar to that of Array.fold and Array.reduce, but the function accepts inputs of any type.

   dale.acc ([1, 2, 3], function (a, b) {return a + b}); // returns 6

   dale.acc ({x: 1, y: 2, z: 3}, function (a, b) {return a + b}); // returns 6

   dale.acc ([1, 2, 3], function (a, b) {return a * b}); // returns 6

   dale.acc ([2, 3], 1, function (a, b) {return a + b}); // returns 6

   dale.acc (['A', 'B', 'C'], function (a, b) {return a + b}); // returns 'ABC';

dale.obj

dale.obj is like dale.go, but it returns an object instead. This function:


var members = [
   {name: 'Pepe', age: 68, active: true},
   {name: 'Dimitri', age: 34, active: false},
   {name: 'Helmut', age: 42, active: true}
];

dale.obj (members, function (v) {
   if (! v.active) return;
   return [v.name, v.age];
});
// returns {Pepe: 68, Helmut: 42}

var base = {
   Fritz: 46,
   Sigfrid: 24
}

dale.obj (members, base, function (v) {
   if (! v.active) return;
   return [v.name, v.age];
});
// returns {Fritz: 46, Sigfrid: 24, Pepe: 68, Helmut: 42}

dale.obj ([], function (v) {
   return [v, v];
});
// returns {}

dale.obj (members, function (v) {
   return /thisisinvalid/
}));
// returns false and prints the following error: `fun passed to dale.obj must return undefined or an array of length 2 but instead returned a value of type regex`

dale.clog (output = dale.obj (members2, function (v) {
   return [1, 2, 3];
}));

// returns false and prints the following error: `fun passed to dale.obj must return undefined or an array of length 2 but instead returned an array of length 0`

Notice that dale.obj always returns an object with zero or more elements, unless one of the invocations to fun returns an invalid value.

One important point: if you pass a base object, the original object will be modified. This means that if you want to preserve the original object, you must either copy it first or avoid using dale.obj.


console.log (base);
// `base` will be equal to {Fritz: 46, Sigfrid: 24, Pepe: 68, Helmut: 42}

dale.times

dale.times is a function that generates an array of numbers - it is an indirect equivalent of a while loop, since it creates an array with consecutive integers [1, 2, ..., n - 1, n] which can then be passed to any of the other functions - most often, dale.go.

The only required parameter is times, which can be either a positive integer or 0, and which states the length of the returned array.

dale.times (3);
// returns [1, 2, 3];

dale.go (dale.times (3), function (v) {return v + 1});
// returns [2, 3, 4];

The default starting value for the first element of the array returned by dale.times is 1. However, this can be changed by passing a second argument, start, to dale.times. start can be either an integer or a float.

dale.times (3, 0);
// returns [0, 1, 2];

dale.times (3, 0.5);
// returns (0.5, 1.5, 2.5);

The default increment used by dale.times is 1. You can change it by passing a third parameter, step, which can be an integer or a float.

dale.times (3, 1, 2);
// returns [1, 3, 5];

dale.times (3, 0, -1);
// returns (0, -1, -2);

dale.times (3, 0, 0);
// returns [0, 0, 0];

Here's how you can use dale.times within the context of other functions.

   // returns [2, 3, 4]
   dale.go (dale.times (3), function (v) {return v + 1}));

   // returns [2, 4]
   dale.fil (dale.times (4), undefined, function (v) {
      if (v % 2 === 0) return v;
   });

   // returns {1: 2}
   dale.obj (dale.times (2), function (v, k) {
      if (v % 2 === 0) return [k, v];
   });

   // returns true
   dale.stop (dale.times (2), false, function (v, k) {
      return v % 3 !== 0;
   });

   // returns false
   dale.stop (dale.times (4), false, function (v, k) {
      return v % 3 !== 0;
   });

   // returns 15
   dale.acc (dale.times (5), function (a, b) {return a + b});

If dale.times receives invalid inputs, it will print an error message and return false.

Inherited properties

By default, dale functions iterate an object, it will only iterate the keys that belong to the object directly, ignoring inherited keys.

   var o1 = {foo: 42}
   var o2 = Object.create (o1);  // o2 inherits from o1

   dale.keys (o1); // returns ['foo']
   dale.keys (o2); // returns []

   dale.go (o1, function (v) {return v});       // returns [42]
   dale.go (o2, function (v) {return v});       // returns []

If you want dale functions to iterate the inherited properties of an object, pass true as the last argument to the function.

   dale.keys (o2, true)                         // returns ['foo']
   dale.go (o2, function (v) {return v}, true); // returns [42]

Logging

For compatibility with old browsers, dale defines and uses dale.clog, a function that will default to console.log and, if console.log is absent, will emit an alert statement instead.

Performance

dale is necessarily slower than a for loop, since it consists of a functional wrapper on top of a for loop. Besides its features, dale's emphasis on code succintness (which is achieved by having a single variadic function generating the main loop) probably adds an extra performance hit.

The benchmark I used is included in example.js - to execute it just run that file, or open it in a browser. The benchmark attempts to make many iterations without almost any computation, to focus on the raw speed of the underlying loop (be it a real loop or dale's layer on top of it).

Testing different versions of node.js and the supported browsers, here's some (very approximate) performance factors:

Iterating arrays:

for:  1x
dale: 2x-9x

Iterating objects:

for:                                    1x
dale:                                   2x-10x
dale, without the hasOwnProperty check: 2x-8x

This means that dale takes roughly twice when iterating arrays and up to ten times more time when iterating objects. Although significant, I believe this is a worthy price to pay for the ease of expression and the facilities provided by dale - especially since many of these facilities have to be inserted into the loops anyway, hence bringing down the speed of a raw for loop.

The modern the javascript engine, the better will dale's performance be relative to that of a for loop.

Source code

The complete source code is contained in dale.js. It is about 160 lines long.

Below is the annotated source.

/*
dale - v6.0.2

Written by Federico Pereiro (fpereiro@gmail.com) and released into the public domain.

Please refer to readme.md to read the annotated source.
*/

Setup

We wrap the entire file in a self-executing anonymous function. This practice is commonly named the javascript module pattern. The purpose of it is to wrap our code in a closure and hence avoid making the local variables we define here to be available outside of this module. A cursory test indicates that local variables exceed the scope of a script in the browser, but not in node.js. This means that this pattern is useful only on the browser.

(function () {

Since this file must run both in the browser and in node.js, we define a variable isNode to check where we are. The exports object only exists in node.js.

   var isNode = typeof exports === 'object';

This is the most succinct form I found to export an object containing all the public members (functions and constants) of a javascript module. Note that, in the browser, we use the global variable dale to export the library.

   if (isNode) var dale = exports;
   else        var dale = window.dale = {};

The type function below is <del>copypasted</del> taken from teishi. This is because I needed dale when writing teishi more than I needed teishi when writing dale. Thus, I decided that teishi should depend on dale. And I don't know if I can elegantly cross-reference both libraries, taking just what I need and avoiding circular dependencies.

The purpose of type is to create an improved version of typeof. The improvements are three:

For the other types that typeof recognizes successfully, type will return the same value as typeof.

type takes a single argument (of any type, naturally) and returns a string with its type.

The possible types of a value can be grouped into three:

If you pass true as a second argument, type will distinguish between plain objects (ie: object literals) and other objects. If you pass an object that belongs to a class, type will return the lowercased class name instead.

The clearest example of this is the arguments object:

type (arguments)        // returns 'object'
type (arguments, true)  // returns 'arguments'

Before we define type, we define argdetect, a local variable that will be true in most javascript engines. In Internet Explorer 8 and below, however, it is not possible to get the type of the prototype of an arguments pseudo-array, hence the definition of this variable (which will be used in type and also once more later).

The variable gets its value from a self-execution anonymous function. We need to do this since the arguments pseudo-array is only defined in the context of a function.

   var argdetect = (function () {return Object.prototype.toString.call (arguments).match ('arguments')}) ();

Below is the function.

   var type = function (value, objectType) {
      var type = typeof value;
      if (type === 'function') return Object.prototype.toString.call (value).match (/regexp/i) ? 'regex' : 'function';
      if (type !== 'object' && type !== 'number') return type;
      if (value instanceof Array) return 'array';
      if (type === 'number') {
         if      (isNaN (value))      return 'nan';
         else if (! isFinite (value)) return 'infinity';
         else if (value % 1 === 0)    return 'integer';
         else                         return 'float';
      }
      if (value === null) return 'null';
      type = Object.prototype.toString.call (value).replace ('[object ', '').replace (']', '').toLowerCase ();
      if (type === 'array' || type === 'date') return type;
      if (type === 'regexp') return 'regex';
      if (objectType) return argdetect ? type : (type (value.callee) === 'function' ? 'arguments' : type);
      return 'object';
   }

We define dale.clog, a function that invokes console.log where available and uses the browser's alert native method otherwise.

   try {
      dale.clog = console.log.bind (console);
   }
   catch (error) {

If we're inside the catch, it means that console might not be supported. It could also be the case that bind is not supported (which happens on browsers without full ES5 support.

      dale.clog = function () {

We construct a string with the message to be printed.

         var output = dale.go (arguments, function (v) {return v === undefined ? 'undefined' : v}).join (' ');

If window.console is available, we invoke it and print output; otherwise, we invoke alert. There's nothing else to do, so we close the function and the catch block.

         window.console ? window.console.log (output) : alert (output);

      }
   }

The main function

All eight functions of dale have many common elements. As a result, I've factored out the common elements in the function make below (short for make function).

make function receives a what argument (can be any of 'go', 'obj', 'fil', 'stop', 'stopNot'). It will then return the corresponding dale function.

dale.keys, dale.times and dale.acc are wrappers around the other functions, so the function below is actually concerned with the other five functions.

   var make = function (what) {
      return function (input, second, third, fourth) {

For dale.go, the arguments received must be input, fun and an optional inherit flag, which must be true. We also set output to an empty array. Finally, we create a variable index to keep track of how many items we added to output array - this is strictly for performance purposes.

         if      (what === 'go')              var fun = second, inherit = third  === true, output = [], index = 0;

For dale.fil, the arguments received must be input, second (which will be the value that must be filtered out), fun and an optional inherit flag. As with dale.go, we set output to an empty array and index to 0.

         else if (what === 'fil')             var fun = third,  inherit = fourth === true, output = [], index = 0;

The case below corresponds both to dale.stop and dale.stopNot, which receive input, second (the value which must be compared to see if the loop has to stop), fun and an optional inherit flag. We define output to be undefined.

         else if (what !== 'obj')             var fun = third,  inherit = fourth === true, output;

If we're here, we're dealing with dale.obj. We will consider the case where we receive a base object between input and fun. In this case, we set output to the argument between input and fun. As with the cases above, we recognize the inherit flag.

         else if (type (second) === 'object') var fun = third,  inherit = fourth === true, output = second;

Finally, we consider the case where dale.obj doesn't receive a base object. In this case, we accept input, fun, inherit and initialize output to an empty object.

         else                                 var fun = second, inherit = third  === true,                     output = {};

We check the type of the arguments. Since input and second can be anything (except for the case of dale.obj, for which we have already checked the type of second), we just need to check that fun is indeed a function.

If fun is not a function, we log an error and return false.

         if (type (fun) !== 'function') {
            dale.clog (((what === 'go' || (what === 'obj' && type (second) !== 'object')) ? 'Second' : 'Third') + ' argument passed to dale.' + what + ' must be a function but instead is', fun, 'with type', type (fun));
            return false;
         }

For any dale function, if the input is undefined, we return the default output. Notice that in this case, the function returns without executing the fun even once.

         if (input === undefined) return output;

We define a local function inner, which we'll execute for each item of output we are iterating. This function takes a single argument, result, which will be the result of applying each element of output to fun.

If inner returns true, this will mean that the iteration process (defined below) will be stopped.

We will define different versions of inner depending on which function we're implementing. Let's start with that for dale.go. In this case, we append result into output and increment index.

         if (what === 'go')       var inner = function (result) {output [index++] = result}

For the case of dale.fil, if result is not equal to second, we append result into output and increment index.

         else if (what === 'fil') var inner = function (result) {
            if (result !== second) output [index++] = result;
         }

For the case of dale.obj:

         else if (what === 'obj') var inner = function (result) {
            if (result === undefined) return;
            if (type (result) !== 'array' || result.length !== 2) {
               dale.clog (type (result) === 'array' ? ('fun passed to dale.obj must return undefined or an array of length 2 but instead returned an array of length ' + result.length) : ('fun passed to dale.obj must return undefined or an array of length 2 but instead returned a value of type ' + type (result)));
               output = false;
               return true;
            }
            output [result [0]] = result [1];
         }

For the case of dale.stop and dale.stopNot, we set output to result. If we're in dale.stop and result is equal to second, we return true to break the loop. We do the same with dale.stopNot when result is not equal to second. Otherwise, we return false, which will do nothing.

         else var inner = function (result) {
            output = result;
            return what === 'stop' ? result === second : result !== second;
         }

We save the type of input in a local variable inputType.

         var inputType = type (input);

If input is an object, we want to check whether this is an arguments object, which we want to treat like an array. To ascertain this we use Object.prototype.toString. We use this method instead of our type function simply for performance purposes. If it is indeed an arguments object, we will convert it into an array.

Note that if argdetect is false (which will happen in IE 8 and below), we check whether input.callee is a function to ascertain whether this is an arguments object. This is a workaround since there seems to be no straightforward way to detect whether a certain object is an arguments object for these particular browsers.

         if (inputType === 'object') {
            if (Object.prototype.toString.call (input) === '[object Arguments]' || (! argdetect && type (input.callee) === 'function')) inputType = 'array', input = [].slice.call (input);
         }

We're ready to iterate input! We first tackle the case where inputType is an array.

         if (inputType === 'array') {

We use a for loop to iterate over input.

            for (var key = 0; key < input.length; key++) {

We call inner passing it result. result will be the result of invoking fun with two arguments: input [key], which is the element being iterated, plus the key. Notice that we apply parseInt to the key. This is because javascript returns stringified numeric iterators ('0', '1', '2'...) when looping an array, instead of numeric keys.

Notice also that the fun receives the value as the first argument and the key as the second. This inversion is useful since usually the fun needs the value but not the key. In this case, with this argument ordering you can write function (v) {...} instead of function (k, v) {...}.

If inner returns true, the iteration will be stopped through a break statement.

There's nothing else to do, so we close the loop and the case.

               if (inner (fun (input [key], parseInt (key)))) break;
            }
         }

If input is an object:

         else if (inputType === 'object') {

We iterate input with a for ... in loop.

            for (var key in input) {

If two conditions are met simultaneously, we skip the current key, by issuing a continue statement. These conditions are:

We also check that input has the hasOwnProperty method. Since input is an object, you would think that it has the hasOwnProperty method. However, when iterating a DOM element's attributes or style object in Internet Explorer 8 and below, the method will be absent despite these objects behaving like plain objects. For this reason, we add this extra check. If the method is absent, we won't skip the key since we have no way of ascertaining whether the object actually contains the key or inherited it.

               if (! inherit && input.hasOwnProperty && ! input.hasOwnProperty (key)) continue;

We now invoke inner with the result of invoking fun with two arguments (the element being iterated, plus its key). If this invocation returns true, we stop the loop with a break statement.

There's nothing else to do, so we close the loop and the case.

               if (inner (fun (input [key], key))) break;
            }
         }

If input is neither an array nor an object, we invoke inner a single time, passing input itself as its first argument and 0 as its second. We pass 0 as the second argument because if input is neither an array nor an object, we consider it to be an array of one element only - hence, the key of its only element will be 0.

There's no point in recording whether the invocation of inner returned true, since we don't need to interrupt an iteration of a single element.

         else inner (fun (input, 0));

At this point, we're done. The return value we need is at output. We return it, then close the function returned by make and make itself.

         return output;
      }
   }

The eight functions

We create each of the dale functions. dale.keys is simply a lambda function that passes input and inherit to dale.go, using a fun that only returns its key.

   dale.go      = make ('go');
   dale.fil     = make ('fil');
   dale.obj     = make ('obj');
   dale.stop    = make ('stop');
   dale.stopNot = make ('stopNot');
   dale.keys      = function (input, inherit) {return dale.go (input, function (v, k) {return k}, inherit)};

dale.times is meant as a replacement for while loops where we iterate through integers. This function takes times (the number of iterations), an optional start parameter to use as the first element of the array and an optional step parameter to specify the increment used.

   dale.times   = function (steps, start, step) {

We validate and initialize the inputs:

If any of these conditions is violated, we print an error message and return false.

      if (steps === 0) return [];
      if (type (steps) !== 'integer' || steps < 0) {
         dale.clog ('steps must be a positive integer or zero.');
         return false;
      }
      if (start === undefined) start = 1;
      else if (type (start) !== 'integer' && type (start) !== 'float') {
         dale.clog ('start must be an integer or float.');
         return false;
      }
      if (step  === undefined) step  = 1;
      else if (type (step) !== 'integer'  && type (step)  !== 'float') {
         dale.clog ('step must be an integer or float.');
         return false;
      }

We initialize output to an array with one element, start.

      var output = [start];

The while loop to end most while loops.

      while (i < steps) {

We increment start by step and then immediately push it onto output. We then close the while loop.

         start += step;
         output.push (start);
      }

We return output and close the function.

      return output;
   }

dale.acc is a function for accumulating results into one, using a function that takes an accumulator (result of previous operations) and a new item on each iteration. It provides the functionality of the functional operations commonly named reduce and fold.

While this function could be possibly inserted into the main function that implements most of the other functions, I felt that its particularities would make the main function more complex and slower, so I opted to write it as a standalone function that calls dale.go in its inner loop.

This function takes up to four arguments.

   dale.acc = function (input, second, third, fourth) {

To determine whether it was passed or not, we count the amount of arguments passed. fun (the following argument) is required, but the inherit flag is also optional. To note whether inherit is passed we check whether the last argument is boolean (since fun cannot be a boolean).

Now, if inherit is not passed, then if there's 3 arguments we will consider acc to be the second one (with fun being the third). If, however, inherit is passed, we'll consider acc to be passed if there's 4 arguments.

      var hasAcc  = arguments.length === (type (arguments [arguments.length - 1]) === 'boolean' ? 4 : 3);
      var acc     = hasAcc ? second : undefined;
      var fun     = hasAcc ? third  : second;
      var inherit = hasAcc ? fourth : third;

We check whether fun is of the right type. Otherwise, we print an error and return false.

      if (type (fun) !== 'function') {
         dale.clog ('fun must be a function but instead is of type', type (fun));
         return false;
      }

We initialize a variable first that will tell us whether we are in the first element of input or not - this is necessary for the case where input is an object.

      var first = true;

We invoke dale.go on our input and a function.

      dale.go (input, function (v, k) {

If no accumulator was passed and we're iterating the first element of input, we set first to false (to mark that we have already processed it) and then we set acc to the value of this element.

         if (! hasAcc && first) {
            first = false;
            return acc = v;
         }

In every other case, we set acc to the value returned by fun when it is passed acc and the element currently being iterated.

         acc = fun (acc, v);

We close the inner loop. Notice we pass the inherit flag to dale.go.

      }, inherit);

We return acc and close the function.

      return acc;
   }

We close the module.

}) ();

License

dale is written by Federico Pereiro (fpereiro@gmail.com) and released into the public domain.