array.length

var t = new Array();
	t[0] = 1;
	t[7] = 2;
	
	alert(t.length); // 8 ??
	alert(t[3]); // Undefined
alert(t[0]); // Undefined
alert(t[x]); // Undefined où <> 0 et 7
alert(t[7]); // 2

0 a 7 --> 8 elements

// show the values stored
for (var i in t) {
	alert('key is: ' + i + ', value is: ' + t[i]);
}

	t[0] = 1;
	t[1] = undefined;
	t[2] = undefined;
	t[3] = undefined;
	t[4] = undefined;
	t[5] = undefined;
	t[6] = undefined;
	t[7] = 2;