exercise-2

Exercise 2

Introduction

Tracking memory leaks is something you should do very rarely. To not say never.

One could build a library which can wrap functions to keep track of all what this function has returned.

Proceed

Start

Using Node 10 or higher, run the exercise code

npm run start-exercise-2

Have a look at the exercise code.

For now, the instrumentation of the library is just a Proxy to its createObject function.

The instrumentation is done by wrapper's wrapFunction function.

Simple retainer

Using an Array, add options to the Proxy constructor to make it store the returned values in a way the exposed logRetainedResults method actually logs them.

Don't hesitate to have a look at the documentation of Proxy.

Also think about editing logRetainedResults!

Solution

const returnValues = [];

const proxy = new Proxy(func, {
  apply(target, thisArg, argumentsList) {
    const returnValue = target.apply(thisArg, argumentsList);
    returnValues.push(returnValue);
    return returnValue;
  },
});

Re-execute the code, and comment the leak.

Too strong!

Edit your last changes to remove the leak.

You may need to change how it logs retained values. Have a look at what is already available in log helper.

Solution

const returnValues = new WeakSet();

const proxy = new Proxy(func, {
  apply(target, thisArg, argumentsList) {
    const returnValue = target.apply(thisArg, argumentsList);
    returnValues.add(returnValue);
    return returnValue;
  },
});