JS Script loader

load-script.js

/**
 * Usage:
 * loadScript('//exmp.com/script.js')
 * loadScript('//exmp.com/script-another.js', function(){runCallback()}, {'data-attribute': 'has'})
 * Will not be loaded, because loaded earlier:
 * loadScript('//exmp.com/script.js')
 **/

/** @type {loadScript} */
var loadScript = (function () {
    var loadedScripts = {},
        jsQueryRegex = /\?[\S\s]+$/

    /**
     * @name loadScript
     * @param {string} src
     * @param {function} [callback]
     * @param {object} [attributes]
     */
    function loadScript(src, callback, attributes) {
        if (typeof callback != 'function') {
            callback = function () {}
        }

        var jsName = src.replace(jsQueryRegex, '')

        if (loadedScripts[jsName] === true) {
            return callback()
        }
        else {
            loadedScripts[jsName] = loadedScripts[jsName] || []
            loadedScripts[jsName].push(callback)
        }

        var script = document.createElement('script')

        if (attributes && attributes instanceof Object) {
            for (var key in attributes) {
                if (attributes.hasOwnProperty(key)) {
                    script.setAttribute(key, attributes[key])
                }
            }
        }

        script.onload = script.onreadystatechange = function() {
            if (this.readyState && !(this.readyState === 'loaded' || this.readyState === 'complete')) {
                return
            }

            var scriptCallbacks = loadedScripts[jsName]

            for (var callback in scriptCallbacks) {
                if (scriptCallbacks.hasOwnProperty(callback)) {
                    scriptCallbacks[callback]()
                    delete scriptCallbacks[callback]
                }
            }

            loadedScripts[jsName] = true

            delete script.onreadystatechange
            delete script.onload
        }

        script.type = 'text/javascript'
        script.src = src

        document.head.appendChild(script)
    }

    return loadScript
})()