/**在抽獎的活動中經常會用到這個算法，不同獎項的獲取概率不同，要按概率去隨機生成對應的獎品**/function random(arr1, arr2) {  var sum = 0,    factor = 0,    random = Math.random();  for(var i = arr2.length - 1; i >= 0; i--) {    sum += arr2[i]; // 統計概率總和  };  random *= sum; // 生成概率隨機數  for(var i = arr2.length - 1; i >= 0; i--) {    factor += arr2[i];    if(random <= factor)      return arr1[i];  };  return null;};// testvar a = ['mac', 'iphone', 'vivo', 'OPPO'];var b = [0.1, 0.2, 0.3, 0.4];console.log(random(a, b));