Append a script tag (legacy way with optional use of jquery)

appendScriptTag.js

/**
 * Creates and appends a script tag to the `document` at `insertLocation`.  (This snippet is a good candidate for adding an
 *  interval or a timeout on the returned $.deffered|HTMLScriptElement)
 * @param options hash of the following parameters:
 *   @param src {String|HTMLScriptElement} - Script source or script element.  Required.
 *   @param doc {document} - `document` object.  Optional.  Default `document`.
 *   @param insertLocation {String} - Location at which to insert the script tag [head,body].  Optional.  Default 'body'.
 *   @param onError {Function} - On error callback.  Optional.  If `$.getScript` is available these callbacks gets passed to `.fail()`.
 *   @param onSuccess {Function} - On success/completion callback.  Optional.
 *   @param useGetScript {Boolean} - Whether to use `$.getScript` if it is available.  Optional.  Default `false`.
 *   **Note If passing true for this parameter then only a `String` `src` parameter will be allowed.
 *   @param logging {Boolean} - Control variable to give the user control from his/her callbacks.  Optional.  Used by internal 'no-op' function.
 * ** To use defaults just pass in `null` for the values you do not want to use (except for the required values).
 * ** Note default logging is false.  If it is set to `true` without passing any callbacks (onSuccess, onError)
 * the error object is logged to the console.
 * @return {mixed|$.deffered|HTMLScriptElement} - If `$.getScript` is not used (see @param comments above) returns
 *  HTMLcriptElement else it returns `$.deffered`.
 */
function appendScriptTag(options) {

    // Prelims
    var isGetScriptAvailable = typeof $ !== 'undefined' && sjl.classOfIs($.getScript, 'Function'),
        scriptTag,
        retVal = null,
        noopCallback = function (e) { if(options.logging) {console.log(e);}},
        src, error, success, doc;

    options = sjl.extend({
        doc: document,
        logging: false,
        insertLocation: 'body',
        useGetScript: false,
        error: noopCallback,
        success: noopCallback,
        src: null
    }, options);

    doc = options.doc;
    src = options.src;
    error = options.error;
    success = options.success;

    // If no `$.getScript` append 'script' tag with vanilla (plain) javascript
    if (!options.useGetScript || !isGetScriptAvailable) {

        // Create script element if none was passed
        if (sjl.classOfIs(src, 'String')) {
            scriptTag = doc.createElement('script');
            scriptTag.src = src;
            scriptTag.onerror = error;
            scriptTag.onload = success;
        }

        // Else assume `src` is a script element
        else {
            scriptTag = src;
        }

        // Insert script tag
        doc[options.insertLocation].appendChild(scriptTag);

        // Exit
        retVal = scriptTag;
    }

    // Append script tag and call callbacks
    return retVal === null ? $.getScript(src, success).fail(error) : retVal;
}