Asynch JSONP handler, w/ ECMA6 Promise

asynch-jsonp-handler-w-ecma6-promise.markdown

Asynch JSONP handler, w/ ECMA6 Promise

This is a refinement to an earlier JSONp handler where I ran into an issue with accessing the response data due to timing. By passing the resolve and reject behaviours to the "then" method the new promise the data object returned in the callback is accessible. http://www.html5rocks.com/en/tutorials/es6/promises/

A Pen by John Lin on CodePen.

License.

script.js

'use strict';
function Omer(uri, qs) {
    //Private QueryString Handler
    function queryString(data) {
        return Object.keys(data).map(function (key) {
            return [key, data[key]].map(encodeURIComponent).join('=');
        }).join('&');
    }
    return new Promise(function(resolve, reject) {
        var tmstp = Date.now(),
            fn = 'ajpRsp_' + tmstp,
            scpe = document.createElement('script'),
            query = qs && typeof qs === 'object' ? '&' + queryString(qs) : '',
            elIDpre = uri.split('//')[1].split('/')[0].split('.')[1],
            url = uri.replace(/callback=\w+/i, 'callback=' + fn);
        url = query ? url + query : url;
        //Private Generic "Callback" method resolves/rejects Promise
        function ajpRsp (tm) {
            return function (data) {
                var ajpCk = false,
                    dtype = typeof data,
                    tid = '#'+tm,
                    rmscr = document.querySelector(tid);
                switch (dtype) {
                    case 'string':
                        ajpCk = JSON.parse(data);
                        break;
                    case 'object':
                        ajpCk = data;
                        break;
                }
                document.querySelector('head').removeChild(rmscr);
                delete window[fn];
                if (ajpCk) {
                    resolve(ajpCk);
                } else {
                    reject(Error('invalid request or empty jsonp object',ajpCk));
                }
            };
        }
        window[fn] = ajpRsp(elIDpre+'_'+tmstp);
        scpe.type = 'text/javascript';
        scpe.src = url;
        scpe.id = elIDpre+'_'+tmstp;
        document.querySelector('head').appendChild(scpe);
    });
}
var test = new Omer('https://public-api.wordpress.com/rest/v1/sites/idcdistro.wordpress.com/posts/?callback=ajpRsp',{});
test.then(postCount).catch(function(error) {
    console.error('Failed!', error);
});

function postCount(data) {
   var p = document.createElement('P'),
        offset = Object.keys(data.posts).length,
        ptxt = document.createTextNode('Successfully found '+offset+' of '+data.found);
    document.body.appendChild(p.appendChild(ptxt));
}