Introduced support to download content as a binary. Minor bug fixes for function signatures

[vgrem]

Introduce a support to download content as a binary

.getBinary

Use .getBinary() to stream a download from Microsoft Graph.

const fs = require('fs'); // requires filesystem module
client
    .api('/me/drive/root/children/Book.docx/content') // path of  source file in OneDrive
    .getBinary((err, buffer) => {
           fs.writeFileSync('Book.docx', buffer,'binary');
    });

[msftclas]

All CLA requirements met.

[MIchaelMainer]

Thank you for the pull request! This will be helpful. I'm sorry but I can't get to this right now. We still need to finish the update to use the Fetch API instead of superagent/xhr. 765594

[muthurathinam]

@vgrem @MIchaelMainer @darrelmiller
This can be achieved by setting responseType to the get call.

client
    .api(`/me/drive/root/children/${fileName}/content`)
    .responseType("blob")
    .get()
    .then((res) => {
        console.log("done");
        console.log(res);
    })
    .catch((err) => {
        throw err;
    });

Do we really need this api change ? -> https://github.com/microsoftgraph/msgraph-sdk-javascript/pull/70/files#diff-28bf2624bd9644553428f50cb8aac3d7R300

[MIchaelMainer]

We don't need it.

Is it discoverable that someone should needs to set the responseType to "blob"? Do we have docs on it. If it isn't, then getBinary may make more sense. We also have a getStream, does that do the same thing?

The easiest thing we can do is update the readme to make it clear how we get binary data.

[muthurathinam]

@MIchaelMainer I agree it is not discoverable as of now. As you mentioned we can update the readme about how to get binary data.
As I am concerned about the size of the output js file, adding such APIs those are achievable in other ways might be unnecessary.
I feel same with the stream APIs, we should have added the guide to achieve that instead of providing new API.

[muthurathinam]

@vgrem @MIchaelMainer

Changes merged with this PR, So closing this one.!!