break和continue的实现

<script type="text/javascript">
var $break = {}, $continue = {};
/*
转：prototype.js
*/

var check = function () {
var a = Array.apply(null, arguments), f = a.shift(), o = a.shift();
try {
f.apply(o, a);
} catch (exp) {
if (exp !== $break) throw exp;
}
};

var each = function (f) {
var a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0], i = 0;

for (; i < a.length ; i ++) {
try {
f(a[i]);
} catch (exp) {
if (exp !== $continue) throw exp;
}
}
};

check(each, null, function (a) {
if (a < 8) {
if (a == 4) throw $continue;
else document.write(a);
} else throw $break;
});
</script>