按给定几率进行随机抽取的js代码

function StringResource(k) { return StringResource[k] || k; } 
function RandomSelector() { 
var f = 0, c = []; return function (v, r) { 
if (arguments.length) { 
if (r <= 0) throw { message: StringResource("INVALID_ARGUMENT") }; 
c.push([r, v]); 
f += r; 
} else { 
var i = 0; r = Math.random() * f; 
for (; ; ) if ((r -= (v = c[i++])[0]) < 0) return v[1]; 
} 
}; 
}