xhr.js

/**
 * Send HTTP requests using XMLHttpRequest
 * @param {string} url The url to which to send the request
 * @param {object} options Configuration like verb and parameters
 * @param {function} callback The function to run after a response is received
 * @returns undefined
 * @example
 * xhr("http://example.com/api/endpoint", { params: { hello: "world", tau: "2pi" } }, function(res, headers) { doStuff(); } );
 */

var xhr = function(url, options, callback) {
    var params, verb;
    
    // check that both args are present and of correct type
    if (!(url && typeof url === "string" && url.length > 0)) {
        throw new Error("missing url");
    }
    
    // set unset options to defaults
    if (!options) {
        options = {};
    }
    if (!options.verb) {
        options.verb = "get";
    }
    if (!options.bodyEncoding) {
        options.bodyEncoding = "application/json";
    }
    if (!callback) {
        callback = function(res, headers) {
            console.log(res);
        }
    }
    
    verb = options.verb.toLowerCase();
    
    // create the XMLHttpRequest and attach load handler
    var req = new XMLHttpRequest();
    req.onload = function() {
        var response = this.response;
        callback(response);
    };
    
    // make parameters string
    if (options.params && options.params instanceof Object && Object.keys(options.params).length > 0) {
        var paramsArray = [];
        
        for (key in options.params) {
            if (options.params.hasOwnProperty(key)) {
                var val = options.params[key];
                paramsArray.push(key + "=" + val);
            }
        }
        
        params = paramsArray.join("&");
    }
    
    req.open(options.verb, url, true);
    
    if (options.verb.toLowerCase() === "get") {
        url += ("?" + params);
        
        req.send();
    } else if (options.verb.toLowerCase() === "post") {
        req.setRequestHeader("Connection", "close");
        
        if (options.bodyEncoding.toLowerCase === "form") {
            req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
            req.setRequestHeader("Content-Length", params.length);
            
            req.send(params);
        } else if (options.bodyEncoding.toLowerCase() === "json") {
            req.setRequestHeader("Content-Type", "application/json");
            
            req.send(options.params);
        }
    }
};