Fetch vs. AjaxCall
What is the difference between typical AJAX and Fetch API?
Consider this scenario:
function ajaxCall(url) {
return new Promise(function(resolve, reject) {
var req = new XMLHttpRequest();
req.open('GET', url);
req.onload = function() {
if (req.status == 200) {
resolve(req.response);
} else {
reject(Error(req.statusText));
}
};
req.onerror = function() {
reject(Error("Network Error"));
};
req.send();
});
}
ajaxCall('www.testSite').then(x => {
console.log(x)
}) // returns html of site
fetch('www.testSite').then(x => {
console.log(x)
}) // returns object with information about call
This is what the fetch
call returns:
Response {type: "cors", url: "www.testSite", status: 200, ok: true, statusText: "OK"…}
Why does it return different things?
Is there a way for fetch
to return the same thing as a typical AJAX call?
Solution 1:
The Fetch API has built in methods for different datatypes.
For just regular text/html you'd use the text()
method, which returns a promise as well, and chain it with another then call.
fetch('www.testSite').then( x => {
return x.text();
}).then( y => {
console.log(y);
});
The built-ins for the returned content is as follows
-
clone()
- Creates a clone of a Response object. -
error()
- Returns a new Response object associated with a network error. -
redirect()
- Creates a new response with a different URL. -
arrayBuffer()
- Returns a promise that resolves with an ArrayBuffer. -
blob()
- Returns a promise that resolves with a Blob. -
formData()
- Returns a promise that resolves with a FormData object. -
json()
- Returns a promise that resolves with a JSON object. -
text()
- Returns a promise that resolves with a USVString (text).
It also allows you to send things to the server, or add your own headers etc.
fetch('www.testSite', {
method : 'post',
headers : new Headers({
'Content-Type': 'application/x-www-form-urlencoded'
}),
body : new FormData(document.getElementById('myform'))
}).then( response => {
return response.json(); // server returned valid JSON
}).then( parsed_result => {
console.log(parsed_result);
});
Solution 2:
Your ajaxCall is returning the responseText from the XMLHttpRequest object. It is filtering it out.
You need to read the response Text in the fetch code.
fetch('/foo/').then(x => x.text()).then(console.log)
You can also use x.json()
or x.blob()