m.request broken for blob data in 2.0.4rc

[CarlLeth]

Mithril Version: 2.0.4rc

request.js, line 118, initializes the response to xhr.responseText before checking for an "extract" function. But the xhr.responseText getter throws an exception (in Chrome, at least) if the response type is anything other than '' or 'text', such as 'blob'. In 1.1.6, providing an extract function properly prevented mithril from calling the xhr.responseText getter.

Steps to Reproduce

Submit

var blobPromise = m.request({
    url: 'an endpoint returning file or blob data',
    config: xhr => xhr.responseType = 'blob',
    headers: { 'Accept': 'octet/stream' },
    extract: xhr => xhr.response
});

Expected Behavior

The returned promise is fulfilled with the blob data.

Current Behavior

Browser error: "Failed to read the 'responseText' property from 'XMLHttpRequest': The value is only accessible if the object's 'responseType' is '' or 'text' (was 'blob')."

Possible Solution

Leave response uninitialized on line 118 of request.js. Set it to xhr.responseText before line 125 instead, and change line 123 to response = args.deserialize(xhr.responseText).

Environment

• Browser: Chrome 71.0.3578.80 (64-bit)

[dead-claudia]

Duplicate of #2333