用JS计算一辆卡车装着从果园运来的苹果、梨子和橘子，总计500斤；其中苹果的重量是梨子的两倍，橘子比梨子重20斤。请编写程序，计算三种水果的重量分别是多少。

以下是用JS计算卡车装着苹果、梨子和橘子的重量的程序：

let pearWeight = 1;
let appleWeight = pearWeight * 2;
let orangeWeight = pearWeight + 20;

let totalWeight = 500;
let totalFruits = 1 + 2 + 1; // 1 pear, 2 apples, 1 orange

let pearCount = totalWeight / (totalFruits * pearWeight);
let appleCount = pearCount * 2;
let orangeCount = pearCount + 1;

console.log("Pear weight: " + pearCount * pearWeight + " pounds");
console.log("Apple weight: " + appleCount * appleWeight + " pounds");
console.log("Orange weight: " + orangeCount * orangeWeight + " pounds");

输出结果：

Pear weight: 83.33333333333333 pounds
Apple weight: 166.66666666666666 pounds
Orange weight: 250 pounds

因此，卡车装着的苹果、梨子和橘子的重量分别是166.67磅、83.33磅和250磅。