【每日一题】- 2019-10-30 实现monitor/unmonitor

[azl397985856]

chrome内置的用来观察函数调用的工具方法。在函数调用的时候，可以同步输出函数名以及参数。当不再需要观察该函数时，调用unmonitor取消即可。

具体用法可以在chrome 的 devtool 自己试试

扩展：

实现chrome下提供的monitorEvents/unmonitorEvents

[azl397985856]

Intuition

We can attach the oldFn onto the newFn which be monitored. If U want to unmonitor it, U can easily take the oldFn back

function monitor(fn) {
  fn.oldFn = fn
  fn = (...args) => {
    console.log(`function ${fn.name} called with arguments: ${args}`);
    oldFn(...args);
  };
}

function unmonitor(fn) {
  fn = fn.oldFn;
}

WA

Actually, It won't work. mmmmmm WHY?

Because JavaScript is copy of reference, So the fn = ... won't change the outside fn. What U really do is allocating a chunk of memory space , and Leave it unchanged.
when the monitor returned, the allocated memory will be freed up. In other words, U do nothing.

What Should I Do

You can never make it . But it will be Very Nice during a interview If U can come up with that, and provide another way which do the same thing