To setup a simple expectation that returns a JSON body for all requests on a given path:

mockServerClient("localhost", 1080).mockSimpleResponse('/somePath', { name: 'value' }, 203);

To setup a more complex expectation:

mockServerClient("localhost", 1080).mockAnyResponse(
    {
        'httpRequest': {
            'method': 'POST',
            'path': '/somePath',
            'queryStringParameters': [
                {
                    'name': 'test',
                    'values': [ 'true' ]
                }
            ],
            'body': {
                'type': 'STRING',
                'value': 'someBody'
            }
        },
        'httpResponse': {
            'statusCode': 200,
            'body': JSON.stringify({ name: 'value' }),
            'delay': {
                'timeUnit': 'MILLISECONDS',
                'value': 250
            }
        },
        'times': {
            'remainingTimes': 1,
            'unlimited': false
        }
    }
);

To setup an expectation that forwards all requests:

mockServerClient("localhost", 1080).mockAnyResponse(
    {
        'httpRequest': {
            'method': 'GET',
            'path': '/somePath'
        },
        "httpForward": {
            "host": "www.mock-server.com",
            "port": 80,
            "scheme": "HTTP"
        },
        'times': {
            'remainingTimes': 1,
            'unlimited': false
        }
    }
);

It is also possible to make AJAX calls directly without the client as follows:

var xmlHttpRequest = new XMLHttpRequest();
xmlHttpRequest.open("PUT", "http://localhost:1080/expectation", false);
xmlHttpRequest.setRequestHeader("Content-Type", "application/json; charset=utf-8");
xmlHttpRequest.send(JSON.stringify({
    "httpRequest": {
        "method": "POST",
        "path": "/login",
        "body": {
            "type": "JSON",
            "value": JSON.stringify({ username: "foo", password: "bar" })
        }
    },
    "httpResponse": {
        "statusCode": 401,
        "headers": [
            {
                "name": "Content-Type",
                "values": ["application/json; charset=utf-8"]
            },
            {
                "name": "Cache-Control",
                "values": ["public, max-age=86400"]
            }
        ],
        "body": JSON.stringify({ message: "incorrect username and password combination" })
    }
}));