Today’s bug in JavaScript code: was using the Array’s join() function and getting results which did not match the expectations. Turns out, that in a case of sparse array (with missing data at certain indexes) join inserts an empty string. So, considering the code:
var a = ['zero', 'one', 'two'];
a[4] = 'four';
alert(a.join(' : '));
The resulting alert will be zero : one : two : : four.
Duh! To adjust to the behavior I have modified the Ruby-like selector to have the «pack» parameter like in this:
// pack is truthy: (default) resets indexes, returns new packed array
// pack is falsy: preserves indexes, returns new sparse array
// tester is a filtering function. Should accept the array's
// element and return truthy or falsy.
Array.prototype['select'] = function(pack, tester){
if (typeof(pack) == 'function') {
tester = pack;
pack = true;
} else if (typeof(tester) != 'function'){
throw { name: 'ArgumentError', message: 'Function expected. Should accept the array\'s element and return truthy or falsy.' }
};
result = [];
for (i in this) {
if ( tester(this[i]) ) {
if (pack) { result.push(this[i]); }
else { result[i] = this[i]; };
};
};
return result;
};
Here are the Firebug runs of the select(...):
>>> [ 1, 2, 3, 4, 5, 6].select( function(e){ return e>3; } )
4,5,6
>>> [ 1, 2, 3, 4, 5, 6].select( false, function(e){ return e>3; } )
,,,4,5,6
>>> [ 1, 2, 3, 4, 5, 6].select( true, function(e){ return e>3; } )
4,5,6
I do not know if this works in all browsers - I have only tested it in Firefox.
2008-12-22