Add fetch support in Ajax

[fuzhenn]

Add support of fetch in Ajax.js if it's available.

XHR missed referer header in HTTP request, fetch can fix this issue.

[nik72619c]

Could you provide the part where it has to be added?

[fuzhenn]

https://github.com/maptalks/maptalks.js/blob/master/src/core/Ajax.js

The fetch support should be smooth and transparent, my thoughts here:

• important to leave methods in Ajax.js unchanged.
• detect fetch support in Browser.js
• switch to fetch if browser supports.
• fall back to xhr if browser doesn't support.

[nik72619c]

Cool...gonna work on this

[nik72619c]

@fuzhenn I guess Browser doesn't use fetch call...could you provide me with the line where the XMLHttpRequest is used?

[nik72619c]

What I think is functions like getClient need to be checked for browser support I am not wrong

[fuzhenn]

Yes, you are right.
We can ignore Browser.js, and do all the things in Ajax.js.