How to improve filters with promises

I had been programming a filters setup for the node API of a MEAN stack app.

Having this ´User´ model:

{[ .=old-user.model.js= | 1.hilite(=javascript=) ]}

It allowed a ´User´ controller like this:

{[ .=old-user.controller.js=| 1.hilite(=javascript=) ]}

The meaning should be straightforward: copy the ´name´ field as is and make the ´admin´ field a proper boolean. That was made possible by this:

{[ .=old-CRUD.controller.js=| 1.hilite(=javascript=) ]}

Then I wanted to add a ´password´ field to the ´User´ model. For storing it I decided to go with Strong Password Hashing with Node.js Standard Library. Properly translated to JavaScript and slightly tweaked I got this:

{[ .=hash.js= | 1.hilite(=javascript=) ]}

So my ´User´ model became this:

{[ .=user.model.js= | 1.hilite(=javascript=) ]}

Have you noticed that the ´Hash´ function relies on the asynchronous´crypto.pbkdf2´ function? That’s just standard, so I wasn’t going to use the synchronous version on a second thought.

Then my problem was:

How do I make these filters work with deferred values?

Ta-da! Promises:

{[ .=user.controller.js= | 1.hilite(=javascript=) ]}

To make that work I had to change a bit the ´CRUD´ controller.

The first change was to separate the filtering from the assignment, so that I could later use the ´Promise.all´ method which allows to synchronize promises and values as well. That implied to pass from a ´CopyFields´ function which filters and assigns each value in turn to a ´FilterFields´ function which filters all values at once, thus making the assignments directly in the ´Create´ function.

{[ .=middle-CRUD.controller.js= | 1.hilite(=javascript=) ]}

The second change was to add a needed special treatment for my promises. You may have noticed that, in the ´case ‘function’:´ above, ´result.value´ can be a promise BUT that won’t make ´result´ a promise itself!! So the code above wouldn’t work yet, because it would complete ´Promise.all´ before getting the hashed password. Finally, I got this:

{[ .=CRUD.controller.js= | 1.hilite(=javascript=) ]}

The added lines make ´result´ a promise if ´result.value´ is one: ´result´ will eventually resolve to the expected result. BTW, the ´stuff.isPromise´ method is the classical ´object.then && typeof object.then == ‘function’´.

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