Eloquent JavaScript 08 Exercises

错误

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Retry

大概率触发MultiplicatorUnitFailure错误，承接直到运行成功并返回结果。

class MultiplicatorUnitFailure extends Error {}

function primitiveMultiply(a, b) {
  if (Math.random() < 0.2) {
    return a * b;
  } else {
    throw new MultiplicatorUnitFailure("Klunk");
  }
}

function reliableMultiply(a, b) {
  // Your code here.
  for(;;){
    try{
      var ans = primitiveMultiply(a,b);
      break;
    }catch(e){
      if(e instanceof MultiplicatorUnitFailure){
        console.log(e);
      }else {
        throw e;
      }
    }
  }
  return ans;
}

console.log(reliableMultiply(8, 8));
// → 64

The locked box

先开锁，不管之后干什么都要在函数执行完毕返回前锁上盒子，因为中间操作可能抛出异常导致后面函数不执行，用finally执行关闭函数即可。

const box = new class {
  locked = true;
  #content = [];

  unlock() { this.locked = false; }
  lock() { this.locked = true;  }
  get content() {
    if (this.locked) throw new Error("Locked!");
    return this.#content;
  }
};

function withBoxUnlocked(body) {
  // Your code here.
  box.unlock();
  try{
    body();
  }catch(e){
    throw e;
  }finally{
    box.lock();
  }
}

withBoxUnlocked(() => {
  box.content.push("gold piece");
});

try {
  withBoxUnlocked(() => {
    throw new Error("Pirates on the horizon! Abort!");
  });
} catch (e) {
  console.log("Error raised: " + e);
}
console.log(box.locked);
// → true