Question

86

Node.js / Express.js - How to override/intercept res.render function?

rated 0 times [ 90] [ 4] / answers: 1 / hits: 21819 / 13 Years ago, tue, february 14, 2012, 12:00:00

I'm building a Node.js app with Connect/Express.js and I want to intercept the res.render(view, option) function to run some code before forwarding it on to the original render function.

app.get('/someUrl', function(req, res) {



    res.render = function(view, options, callback) {

        view = 'testViews/' + view;

        res.prototype.render(view, options, callback);

    };



    res.render('index', { title: 'Hello world' });

});

It looks like a contrived example, but it does fit in an overall framework I'm building.

My knowledge of OOP and Prototypal inheritance on JavaScript is a bit weak. How would I do something like this?

Update: After some experimentation I came up with the following:

app.get('/someUrl', function(req, res) {



    var response = {};



    response.prototype = res;



    response.render = function(view, opts, fn, parent, sub){

        view = 'testViews/' + view;

        this.prototype.render(view, opts, fn, parent, sub);

    };



    response.render('index', { title: 'Hello world' });

});

It seems to work. Not sure if it's the best solution as I'm creating a new response wrapper object for each request, would that be a problem?

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zayne

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3 Years ago

answered 13 Years ago jazminuniquer · Accepted Answer

Old question, but found myself asking the same thing. How to intercept res render?
Using express 4.0x something now.

You can use/write middleware. The concept was a bit daunting to me at first, but after some reading it made a little more sense. And just for some context for anyone else reading this, the motivation for overriding res.render was to provide global view variables. I want session to be available in all my templates without me having to type it in every res object.

The basic middleware format is.

app.use( function( req, res, next ) {

    //....

    next();

} );

The next param and function call are crucial to execution. next is the callback function, to allow multiple middleware to do their thing without blocking. For a better explanation read here

This can then be used to override render logic

app.use( function( req, res, next ) {

    // grab reference of render

    var _render = res.render;

    // override logic

    res.render = function( view, options, fn ) {

        // do some custom logic

        _.extend( options, {session: true} );

        // continue with original render

        _render.call( this, view, options, fn );

    }

    next();

} );

I've tested this code, using express 3.0.6. It should work with 4.x without issue.
You can also override specific URLs combos with

app.use( '/myspcificurl', function( req, res, next ) {...} );