Different JS tricks, features, etc.

JSTricks.js

// Check if variable is array or object
// (From underscore.js each() implementation)

var array = [];
var object = {a:1,b:2};


if (obj == null) return;
//actually it is logically equivalent to this ugliness:  if ((obj === null) || (obj === undefined))


if (obj.forEach && obj.forEach === Array.prototype.forEach) {
	// array, native forEach looping
} else if (obj.length === +obj.length) {
	// very nerdy.
	// IF this is array, integer === +integer, it passes here. 
	//     The lowest length array can have is 0.
	// IF this is object, however...
	// obj.length = undefined,  +obj.length = +undefined = NaN 
	//     undefined !== NaN
} else {
	// ... is object
}

//==========================================================================================================================
// Accessor Properties example - temperature converter
// Crockford's Accessor properties example
// from "Crockford on JavaScript - Chapter 2: And Then There Was JavaScript"
// http://www.youtube.com/watch?v=RO1Wnu-xKoY
var temperature_converter = {};
(function(converter) {
        Object.defineProperty(converter, 'F', {
		get: function () {
			return parseFloat((((this.C * 9) / 5) + 32).toFixed(2));
		},
		set: function (value) {
			this.C = parseFloat(((value - 32) * (5 / 9)).toFixed(2));
		},
		enumerable: true
	});
})(temperature_converter);

// This converter works both ways.
// If you set C first, just by getting F, 
// you just end up calling get() accessor property

// If you set F first, set() gets called, setting C.

temperature_converter.F = 100; 
//temperature_converter.C returns 37.75
temperature_converter.C = 200
//temperature_converter.F returns 392


// Crockford's Accessor properties example
// from "Crockford on JavaScript - Chapter 2: And Then There Was JavaScript"
// http://www.youtube.com/watch?v=RO1Wnu-xKoY
// (added float and toFixed)
var distance_converter = {};
(function(converter) {
	Object.defineProperty(converter, 'inch', {
		get: function () {
			return parseFloat((this.mm / 25.4).toFixed(2));
		},
		set: function (value) {
			this.mm = parseFloat((value * 25.4).toFixed(2));
		},
		enumerable: true
	});
})(distance_converter);

distance_converter.mm = 100;
//distance_converter.inch = 3.94

switch.conditional_to_object.js

clear();

function toType (obj) {
  return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}

var test = {
    "array": function() {
		console.log("ARRAY");
	},
	"object": function() {
		console.log("OBJECT");
	},
	"default": function() {
		console.log("DEFAULT");
	}
}

var data = ""; // => DEFAULT, [] => ARRAY, {} => OBJECT
var gear = test[toType(data)] || test["default"];
gear();

underscore_group_by.js

var nativeForEach = Array.prototype.forEach,
breaker = {};

var each = function(obj, iterator, context) {
    if (obj == null) return;
    if (nativeForEach && obj.forEach === nativeForEach) {
      obj.forEach(iterator, context);
    } else if (obj.length === +obj.length) {
      for (var i = 0, l = obj.length; i < l; i++) {
        if (iterator.call(context, obj[i], i, obj) === breaker) return;
      }
    } else {
      for (var key in obj) {
        if (obj.hasOwnProperty(key)) {
          if (iterator.call(context, obj[key], key, obj) === breaker) return;
        }
      }
    }
  };


function group (list, value, context) {
  var result = {};
	//var iterator = value; // or wrap to function
	each(list, function(object, index) {
		var key = value.call(context, object);
		if (!result.hasOwnProperty(key)) {
			result[key] = [];
		}
		result[key].push(object);
	});
	return result;
}


var collection = [
	{a:3,b:2,color:"green"}, 
	{a:3,b:4,color:"green"}, 
	{a:3,b:5,color:"blue"},
	{a:3,b:8,color:"blue"}
];

group(collection, 
	  function(object) { return object.color; }
	  );