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();
} );

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