function myRandom() { var rand = Math.random(); if (rand < .5) return 1; if (rand < .8) return 2; if (rand < .95) return 3; return 5;}

function prizeRand(oArr) { var sum = 0; // 總和 var rand = 0; // 每次循環產生的隨機數 var result = 0; // 返回的對象的key console.log(oArr); // 計算總和 for (var i in oArr) {  sum += oArr[i][0]; } // 思路就是如果設置的數落在隨機數內，則返回，否則減去本次的數 for (var i in oArr) {  rand = Math.floor(Math.random()*sum + 1);  if (oArr[i][0] >= rand) {   result = oArr[i][0];   break;  } else {   sum -= oArr[i][0];  } } return result;}var oArr = {'5':[5, 'Mac'], '3':[15, 'iPhone'], '2':[30, 'iPad'], '1':[50, 'iWatch']};console.log(prizeRand(oArr));