如何判断是否从fetch（）调用了页面？

With jQuery the Ajax function sets the header HTTP_X_REQUESTED_WITH , so with PHP I could do:

if(filter_input(INPUT_SERVER, 'HTTP_X_REQUESTED_WITH') === 'XMLHttpRequest')
{ ... }

And this will tell me the page has been requested using Ajax.

Now I'm wanting to change the Ajax function to fetch(). I've looked through the default headers that it sets and I can't find anything that I can use to to tell if the request is being sent from a fetch.

I could set the header myself:

fetch('/get/login', {
    headers: {
        'X-Requested-With': 'fetch',
    },
})
.then(function(response) { ... }

However it isn't ideal to be writing that header out for every fetch. What are my options here? Is there a better way to tell if the request is being made through a fetch?

No, there is nothing else you can rely on.

Theoretically you shouldn't give your server different behaviour depending on request method; that should be orthogonal to the content defined by your system's back-end.

But, if you're desperate, I quite like your existing solution; you could wrap it in a function for brevity.

Since you are relying on the client side to pass the data, couldn't you pass a POST variable inside body? Passing a header via javascript is no more secure than simply passing an additional field. (https://davidwalsh.name/fetch)

fetch('/get/login', {
    body: JSON.stringify({
        source: : "fetch"
    }),
})
.then(function(response) { ... }