Add utm params to link

gistfile1.js

var qs = require('qs')
var url = require('url')

var add_utm_params_to_link = function(link, utm_source, utm_medium, utm_content, utm_campaign) {
    var parsed = url.parse(link)
    var query = qs.parse(parsed.query)

    query.utm_source = utm_source
    query.utm_medium = utm_medium
    query.utm_content = utm_content
    query.utm_campaign = utm_campaign

    parsed.search = qs.stringify(query)

    return url.format(parsed)
}