multi-dimensional-object-from-form-input-fields.js

var data = {}
	, fields = [
		'earth[africa][sudan][lion]'
		, 'earth[africa][sudan][girafe]'
		, 'earth[africa][sudan][monkeys][lemur]'
		, 'earth[africa][zimbabwee][elephants]'
		, 'earth[africa][zimbabwee][elephants]'
		, 'earth[africa][zimbabwee][elephants]'
		, 'earth[europe][switzerland][chocolate]'
		, 'pluto[isnt][a][planet]'
		, 'sun'
		, 'Things.stuff.nicknacks.fizzldie_wacks'
		]
	, re = /(\w+)/g
	;

fields.forEach(function(v, _i) {
	var p
		, matches = v.match(re)
		, length = matches.length
		;
		
	for (var i = 1; i <= length; i++) {
		var k = matches[i - 1]
			, p = p ? p : data
			;

		if ('undefined' === typeof p[k]) p[k] = length === i ? 'thevalue' : {};
		else if (length === i) {
			if ('object' === typeof p[k]) p[k].push('thevalue3');
			else p[k] = [p[k], 'thevalue2'];
		}

		p = p[k];
	}
});

console.log(JSON.stringify(data, true, '	'));
console.log(data);