Sinon: TypeError: Attempted to wrap undefined property undefined as function

[lizlux]

When trying to use the example code from http://sinonjs.org/docs/#server, I get the following error: TypeError: Attempted to wrap undefined property undefined as function.

Here's the function I'm trying to test:

function xhrPost(url, options) {
    let xhr = new XMLHttpRequest();
    let {data, success, fail} = options;

    if (!url || !isString(url)) {
        throw new TypeError('URL string must be provided for an xhr call');
    }

    xhr.open('POST', url, true);
    xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');

    if (success) {
        xhr.addEventListener('load', success);
    }
    if (fail) {
        xhr.addEventListener('error', fail);
    }
    if (data) {
        data = serializeRequestData(data);
    }

    xhr.send(data || null);
}

The unit test code is:

QUnit.module('utils', {
    beforeEach() {
        // copy/pasteed from example in docs
        let requests = this.requests = [];
        this.xhr = sinon.useFakeXMLHttpRequest();
        this.xhr.onCreate = function (xhr) {
            requests.push(xhr);
        };
    },

    afterEach() {
        // copy/pasteed from example in docs
        this.xhr.restore();
    }
});

QUnit.test('xhr helper function', function (assert) {
    xhrPost('/api.php', {
        data: {
            title: 'foo'
        },
        success: sinon.spy,
        fail: sinon.spy
    });

    // copy/pasted from example in docs
    this.requests[0].respond(200, { "Content-Type": "application/json" },
        '[{ "id": 12, "comment": "Hey there" }]');
    assert(callback.calledWith([{ id: 12, comment: "Hey there" }]));
});

The fake request goes through without issues, but when I call respond(), I get the above error. If I comment out the success and fail functions of xhrPost, I don't get an error. The problem seems to stem from a combination of calling respond with onerror or onfail events (and I did tried switching to onerror and onfail instead of addEventListener but no dice).

This seems to me like a bug in the code, but please let me know if I'm doing something wrong. Thanks!

[lizlux]

And, I answered my own question. Should be invoking sinon.spy, like:

```es6 xhrPost('/api.php', { data: { title: 'foo' }, success: sinon.spy(), fail: sinon.spy() });

Closing the issue!
``````