//create myData object as shown in question
myData = {};
myData[1] = 'hello';
myData[2] = 'goodbye';
myData[3] = {};
myData[3][1] = 'sub1';
myData[3][2] = 'sub2';
myData[3][3] = 'sub3';

//create config object for use with source code
config = {};
config.data = myData;

//execute source code snippet

var pairs = [];
for (var key in config.data) {
    if (config.data.hasOwnProperty(key)) {
        pairs.push(encodeURIComponent(key) + "=" + encodeURIComponent(config.data[key]));
    }
}
var data = pairs.join("&");

//
console.log(data);

//result
1=hello&2=goodbye&3=%5Bobject%20Object%5D