Tips for using res.json as a callback function

When using a function with a callback parameter, I found that this method works perfectly fine:

DB.last(user,(data) => res.json(data));
However, when attempting to refactor it for better readability as shown below: DB.last(user,res.json);

The structure of DB.last is as follows:

  static last(user, callback) {
    let data = {name: user, registered: new Date()};
    callback(data);
  }

This specific function call of DB.last is within an express router script.

While there seems to be a clear distinction between the two approaches, it makes sense to me to pass res.json as a callback parameter to my DB module (considering functions can be passed in JavaScript), but unfortunately, this approach doesn't work as expected.

What could be causing this issue and why isn't it functioning properly?

Answer №1

In order to utilize res.json.bind(res), you must call res.json().

When res.json() is invoked, it operates on the res object (specifically, this pertains to res at the time of execution). However, if you pass res.json as a parameter for a callback function, and then invoke it as callback(), the operation will take place with regard to the context that defines what this means within callback().

To ensure that the function is always called in relation to res, use the bind() method. By doing this, every time the bound function is called, its reference to this will consistently be associated with res.

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