UPDATE 11/28:(更新11/28：)
Problem resolved.(问题已解决。)
It was in fact a completely different problem, irrelevant to fetch/ajax/etc, but unwanted object update via reference.(实际上，这是一个完全不同的问题，与fetch / ajax / etc不相关，但是不需要通过引用来更新对象。)
What misled me was that the actual code I use has a subsequent step after console.log.(误导我的是，我使用的实际代码在console.log之后有一个后续步骤。)
That subsequent step altered the data json, and as a consequence console.log value changed.(随后的步骤更改了数据json，结果console.log值也更改了。) It's fixed by deep clone the json.(可以通过深度克隆json来解决。)
What remains unsure to me is that why console.log comes before the data alteration but is affected -- guess console.log is async in this case.(我仍然不确定的是，为什么console.log在数据更改之前出现但受到影响-猜测在这种情况下console.log是异步的。)
=================== Original:(===================原始：)
Super weird problem.(超级怪异的问题。)
My frontend needs to GET data from backend, so I used fetch in a promise chaining style, such as(我的前端需要从后端获取数据，因此我以承诺链接的方式使用了访存，例如)
fetch(myUrl, {credntials: 'include'})
.then(res=>{
if(res.status==200){
return res.json()
}
else{
return null
}
})
.then(json=>{
if(json){
console.log(json)
}
})
Seems to be working fine and I got some data back.(似乎工作正常，我得到了一些数据。)
However, I noticed that the resolved JSON is different from the expected response from backend.(但是，我注意到解析的JSON与后端的预期响应不同。) For example, the backend outputs {'a': {'aa':1, 'bb':1}} , and the resolved res.json() gives me something like {'a': {'aa':2, 'bb':1}} .(例如，后端输出{'a': {'aa':1, 'bb':1}} ，解析的res.json()给我类似{'a': {'aa':2, 'bb':1}} 。) The change seems to be inconsistent, I got different res.json() value when tried again and again.(更改似乎不一致，一次又一次尝试时，我得到了不同的res.json()值。)
I then tried several different way to GET data:(然后，我尝试了几种不同的获取数据的方式：)
1) typed in url in browser address bar => got correct data(1）在浏览器地址栏中输入url =>获得正确的数据)
2) use jQuery ajax method instead of fetch => got correct data(2）使用jQuery ajax方法而不是fetch =>获得正确的数据)
3) change promise chaining to async/await => this got correct data too!(3）将诺言链更改为异步/等待=>这也获得了正确的数据！)
let resp = await fetch(myUrl, {credentials: 'include'})
let json = await resp.json()
console.log(json)
4) tried the promise chained fetch, still incorrect data!(4）尝试了诺言链式获取，仍然是错误的数据！)
Super confused.(超级困惑。)
Am I using fetch wrong?(我使用提取错误吗？) Is it a bug?(是虫子吗？) Is it the browser?(是浏览器吗？) Is it the polyfill (I'm using "whatwg-fetch": "3.0.0" , but on Chrome, Mac, which in theory the polyfill should not affect anything at all)?(是"whatwg-fetch": "3.0.0" （我使用的是"whatwg-fetch": "3.0.0" ，但是在Chrome，Mac上，从理论上讲，polyfill完全不会影响任何东西）？) Is it response header settings (Django, JsonResponse)?(它是响应标头设置（Django，JsonResponse）吗？) Has anyone had similar experience?(有没有人有类似的经历？)
Update: attach the headers(更新：附加标题)
Request URL: ...
Request Method: GET
Status Code: 200 OK
Remote Address: 127.0.0.1:8000
Referrer Policy: no-referrer-when-downgrade
Response Headers:
HTTP/1.1 200 OK
Date: Wed, 27 Nov 2019 19:39:26 GMT
Server: WSGIServer/0.2 CPython/3.6.6
Content-Type: application/json
Allow: GET, HEAD, OPTIONS
Content-Length: 1559
Vary: Origin, Cookie
Request Headers:
GET ... HTTP/1.1
Host: 127.0.0.1:8000
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36
Accept: */*
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Referer: http://127.0.0.1:8000/...
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9,zh-CN;q=0.8,zh-TW;q=0.7,zh;q=0.6
Cookie: ...
When I check the Preview and Response in chrome developer tools, both of them show correct data.(当我在chrome开发人员工具中检查“ Preview和“ Response时，它们都显示正确的数据。)
However the console.log(json) line outputs differently.(但是console.log(json)行的输出不同。)
ask by rollerCoaster translate from so
