A contrived example of a function for templating javascript files in javascript. The `__compile__` function extracts the function body of a passed in anonymous function, then (optionally) replaces keywords (e.g., __foo__) with properties from a passed in object.

__compile__.js

/** 
 * given a function, strips out its body code and optionally replaces
 * template tags (variable names surrounded by double-underscores, 
 * e.g., __foo__) replacing them with values from a passed in object
 */
__compile__ = function (fnc, obj) {
    var body = fnc.toString().match(/^function\s*[0-9a-zA-Z_$]*\s*\([\w\s,\$_]*\)\s*\{(?:\s*\n?)?([\w\W\s]*)\n?\}$/m)[1]
    if (obj === undefined)
        return body

    var matches = body.match(/(__[0-9a-zA-Z_$]*__)+/gm)
    var i = matches.length
    var matchedKeys = {}
    var key, key2
    while (i-- > 0) {
        key = matches[i]
        if (key.length < 5 || typeof matchedKeys[key] !== 'undefined')
            continue
        key2 = key.substr(2, key.length - 4)
        if (typeof obj[key2] === 'undefined')
            throw 'Undefined replacement ' + key

        matchedKeys[key] = key2
        body = body.replace(new RegExp(key, 'g'), obj[key2])
    }
    return body
}

/**
 * example use - defining a template, then rendering out a few copies of it
 */
var queryTemplate = function () {
    exports.__method__ = function (req, res, next) {
      var db = req.openMysqlConnection()
      var sql = "__query__"
      var params = [__params__]

      db.query(sql, params, function(err, rows){
        if (err) throw err
        res.write(JSON.stringify(rows))
      })

      db.end(function(err){
        if (err) throw err
        res.end()
      })
    }
}

__compile__(queryTemplate, {
    method: 'getFoo',
    query: "SELECT * FROM foo WHERE id = ?",
    params: 'req.body.id'
})

__compile__(queryTemplate, {
    method: 'insertFoo',
    query: "INSERT INTO foo SET bar = ? ",
    params: 'req.body.bar'
})

__compile__(queryTemplate, {
    method: 'updateFoo',
    query: "UPDATE foo SET bar = ? WHERE id = ?",
    params: 'req.body.bar, req.body.id'
})

__compile__(queryTemplate, {
    method: 'deleteFoo',
    query: "DELETE FROM foo WHERE id = ?",
    params: 'req.body.id'
})