Conditionally chain functions in JavaScript

Question

I'm trying to refactor the following node.js code.

Each case generates a thumbnail, chaining a different set of GraphicMagic transformation to an image.

switch(style.name) {
    case 'original':
        gm(response.Body)
            .setFormat('jpg').autoOrient().resize(style.w, style.h, style.option)
            .toBuffer(function(err, buffer) { if (err) { next(err); } else { next(null, buffer); } });
        break;
    case 'large':
        gm(response.Body)
            .setFormat('jpg').autoOrient().resize(style.w, style.h, style.option)
            .quality(style.quality)
            .strip().interlace('Plane')
            .toBuffer(function(err, buffer) { if (err) { next(err); } else { next(null, buffer); } });
        break;
    case 'medium':
        gm(response.Body)
            .setFormat('jpg').autoOrient().resize(style.w, style.h, style.option)
            .crop(style.w, style.h, style.crop.x_offset, style.crop.y_offset)
            .repage('+')
            .strip().interlace('Plane')
            .toBuffer(function(err, buffer) { if (err) { next(err); } else { next(null, buffer); } });
        break;
    case 'small':
        gm(response.Body)
            .setFormat('jpg').autoOrient().resize(style.w, style.h, style.option)
            .crop(style.w, style.h, style.crop.x_offset, style.crop.y_offset).repage('+')
            .quality(style.quality)
            .strip().interlace('Plane')
            .toBuffer(function(err, buffer) { if (err) { next(err); } else { next(null, buffer); } });
        break;
}

However, all cases share a number of transformations at the beginning and the end of the chaining, so there's room for refactoring. I tried refactoring with the following approach, but the code seems incorrect:

gm(response.Body)
.setFormat('jpg').autoOrient().resize(style.w, style.h, style.option, function(err, response) {
    if (style.name === 'original'){
        return response;
    } else if (style.name === 'large'){
        return response.quality(style.quality)
    } else if (style.name === 'medium'){
        return response.crop(style.w, style.h, style.crop.x_offset, style.crop.y_offset).repage('+')
    } else if (style.name === 'small'){
        return response.crop(style.w, style.h, style.crop.x_offset, style.crop.y_offset).repage('+').quality(style.quality)
    }
}).(function(response) {
    return (stryle.name !== 'original') ? response.strip().interlace('Plane') : return response;
}).(function(argument) {
    return response.toBuffer(function(err, buffer) { if (err) { next(err); } else { next(null, buffer); } });
});

Answer 1

I wouldn't go for a switch at all.

There is no reason to use chaining at all here. Just do

// if (!/^(original|large|medium|small)$/.test(style.name)) throw new Error(…);
var x = gm(response.Body)
         .setFormat('jpg')
         .autoOrient()
         .resize(style.w, style.h, style.option);
if (style.name == "medium" || style.name == "small")
    x = x.crop(style.w, style.h, style.crop.x_offset, style.crop.y_offset)
         .repage('+');
if (style.name == "large" || style.name == "small")
    x = x.quality(style.quality);
if (style.name == "large" || style.name == "medium" || style.name == "small")
// possibly better than if (style.name != "original")
    x = x.strip()
         .interlace('Plane');
x.toBuffer(next);

But if you're having a large set of options so that it gets unreadable, better factor out each transformation in a function:

function resizedJpg(x) {
    return x.setFormat('jpg').autoOrient().resize(style.w, style.h, style.option);
}
function cropped(x) {
    return x.crop(style.w, style.h, style.crop.x_offset, style.crop.y_offset).repage('+');
}
function withQuality(x) {
    return x.quality(style.quality);
}
function stripped(x) {
    return x.strip().interlace('Plane');
}

And then apply them separately:

({
    original: [resizedJpg],
    large:    [resizedJpg,          withQuality, stripped],
    medium:   [resizedJpg, cropped,              stripped],
    small:    [resizedJpg, cropped, withQuality, stripped]
}[style.name]).reduce(function(x, trans) {
    return trans(x);
}, gm(response.Body)).toBuffer(next);