How to declare a function that can be called from any view in express js?

Question

Is it possible to create a function somewhere that can be called from any view in my express js mvc web app? How to declare such function in middleware to be accessed directly from a view?

So I can call this function like:

<%= getVar('my_name') %> // calling from the view 

and implement return logic of the variable where the function is declared. This function may use request and response objects.

Note: 'my_name' can be anything on the view which cannot be assigned from the controller.

Answer 1

You can add functions to app.locals or res.locals just like you would add variables to it. If you want to have the request and response available in there (which, frankly, I feel bleeds a bit into what your controllers should be doing), you could create a middleware and pass those in.

From what you said in your comment, it's actually best to just set the variable that the view can use, eg:

app.use((req, res, next) => {
   res.locals.value = req.session.value || 'default value';
   next();
});

if you really need the function to be usable in the view, you can set it the same way, and bind the request and response to the function if needed:

function getVar(req, res, anotherArg) {
   // do whatever
}

app.use((req, res, next) => {
   res.locals.getVar= getVar.bind(null, req, res);
   next();
});