<div> <button id="test-promise-log">log</button> </div> <script> var logging = document.getElementById('test-promise-log'); while (logging.children.length > 1) { logging.removeChild(logging.children[logging.children.length - 1]); }

    function log(s) {
        var p = document.createElement('p');
        p.innerHTML = s;
        logging.appendChild(p);
    }
    new Promise(function(resolve, reject) {
        log('start new Promise...');
        var timeOut = Math.random() * 2;
        log('set timeout to: ' + timeOut + 'seconds.');
        setTimeout(function() {
            if (timeOut < 1) {
                log('call resolve()...            ');
                resolve('200 OK ');
            } else {
                log('call reject()...');
                reject('timeout in ' + timeOut + ' seconds.');
            }
        }, timeOut * 1000);
    }).then(function(r) {
        log('Done: ' + r);
        return new Promise(function(resolve, reject) {
            log('Done2: ' + r);
            resolve('300 OK ');
        });
    }).catch(function(reason) {
        log('Failed: ' + reason);
        return new Promise(function(resolve, reject) {
            log('Failed2: ' + reason);
            reject('timeout in ' + timeOut + ' seconds.');
        });
    }).then(function(r) {
        log('Done3: ' + r);
    }).catch(function(reason) {
        log('Failed3: ' + reason);
    });
</script>