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fetch is the new XHR
othree @ coscup 2015
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XHR
• XMLHttpRequest
• by Microsoft, 1999
• Make HTTP request in web page
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Ajax
• Most popular pattern based on XHR
• Jesse James Garrett named it “AJAX”
• Foundation of Single Page Application
http://www.adaptivepath.com/ideas/ajax-new-approach-web-applications/
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XHR Spec
• W3C Working Draft since 2006, Level 2 since
2008
• WHATWG Living Standard since 2011
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What’s in 2.0
CORS FormData
ArrayBuffer File/Blob
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function uploadFiles(url, files) {
var formData = new FormData();
for (var i = 0, file; file = files[i]; ++i) {
formData.append(file.name, file);
}
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.onload = function(e) { ... };
xhr.send(formData); // multipart/form-data
}
document.querySelector('input[type="file"]')
.addEventListener('change', function(e) {
uploadFiles('/server', this.files);
}, false);
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function uploadFiles(url, files) {
var formData = new FormData();
for (var i = 0, file; file = files[i]; ++i) {
formData.append(file.name, file);
}
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.onload = function(e) { ... };
xhr.send(formData); // multipart/form-data
}
document.querySelector(‘input[type="file"]')
.addEventListener('change', function(e) {
uploadFiles('/server', this.files);
}, false);
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function uploadFiles(url, files) {
var formData = new FormData();
for (var i = 0, file; file = files[i]; ++i) {
formData.append(file.name, file);
}
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.onload = function(e) { ... };
xhr.send(formData); // multipart/form-data
}
document.querySelector(‘input[type="file"]')
.addEventListener('change', function(e) {
uploadFiles('/server', this.files);
}, false);
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function uploadFiles(url, files) {
var formData = new FormData();
for (var i = 0, file; file = files[i]; ++i) {
formData.append(file.name, file);
}
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.onload = function(e) { ... };
xhr.send(formData); // multipart/form-data
}
document.querySelector(‘input[type="file"]')
.addEventListener('change', function(e) {
uploadFiles('/server', this.files);
}, false);
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function uploadFiles(url, files) {
var formData = new FormData();
for (var i = 0, file; file = files[i]; ++i) {
formData.append(file.name, file);
}
var xhr = new XMLHttpRequest();
xhr.open('POST', url, true);
xhr.onload = function(e) { ... };
xhr.send(formData); // multipart/form-data
}
document.querySelector(‘input[type="file"]')
.addEventListener('change', function(e) {
uploadFiles('/server', this.files);
}, false);
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XHR
• 15 years old
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赫⻔门 at ShenJS
ૄϖᇀؽඹ۱ᄅđభ؊߶၂П
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128x harder than 15 years ago
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New Stuffs
JSON FormData File/Blob
Promise ServiceWorker ArrayBuffer
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Not every new tech can apply to XHR without
break it.
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So here is the new XHR.
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Fetch
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Fetch
• The unified architecture of resource fetching
• img, script, css, cursor image, …etc
• fetch() JavaScript API
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Fetch
• The unified architecture of resource fetching
• img, script, css, cursor image, …etc
• fetch() JavaScript API
Today’s
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fetch
• Promise based
• JSON support
• Simple naming, options object
• Designed as low level API
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fetch('./api/some.json').then(function(response) {
return response.json();
}).then(function(data) {
console.log(data);
});
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fetch('./api/some.json').then(function(response) {
return response.json();
}).then(function(data) {
console.log(data);
});
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fetch('./api/some.json').then(function(response) {
return response.json();
}).then(function(data) {
console.log(data);
});
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fetch('./api/some.json').then(function(response) {
return response.json();
}).then(function(data) {
console.log(data);
});
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fetch('./api/some.txt').then(function(response) {
return response.text();
}).then(function(data) {
console.log(data);
});
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fetch('./api/some.file').then(function(response) {
return response.blob();
}).then(function(data) {
// console.log(data);
});
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fetch('./api/some.json')
.then(res => res.json())
.then(data => console.log(data));
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fetch('./api/entry', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify(data)
}).then(function(response) {
response.json().then(data => console.log(data));
return response;
});
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fetch('./api/entry', {
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-url-encoded'
},
body: $.param(data)
});
http://api.jquery.com/jquery.param/
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fetch('./api/entry', {
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-url-encoded'
},
body: $.param(data)
});
http://api.jquery.com/jquery.param/
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fetch('./api/entry', {
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-url-encoded'
},
body: $.param(data)
});
http://api.jquery.com/jquery.param/
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var obj = { key1: 'value1', key2: [10, 20, 30] };
var str = $.param(obj);
// "key1=value1&key2%5B%5D=10&key2%5B%5D=20&key2%5B%5D=30"
https://www.npmjs.com/package/jquery-param
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var obj = { key1: 'value1', key2: [10, 20, 30] };
var str = $.param(obj);
// "key1=value1&key2%5B%5D=10&key2%5B%5D=20&key2%5B%5D=30"
http://www.w3.org/TR/html5/forms.html#application/x-www-form-urlencoded-encoding-algorithm
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var obj = { key1: 'value1', key2: [10, 20, 30] };
var str = $.param(obj);
// "key1=value1&key2%5B%5D=10&key2%5B%5D=20&key2%5B%5D=30"
// key1=value1 &
// key2[]=10 &
// key2[]=20 &
// key2[]=30
http://www.w3.org/TR/html5/forms.html#application/x-www-form-urlencoded-encoding-algorithm
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Or you can post JSON, or other format
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fetch('./api/entry', {
method:'POST',
headers: {
'Content-Type': 'application/x-www-form-url-encoded'
},
body: $.param(data)
});
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method headers
body mode
crendentials cache
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method headers
body mode
crendentials cache
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mode
• The one XHR can’t do
• same-origin
• cors
• no-cors
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no-cors
• Don’t check CORS
• Get opaque response
• For ServiceWorker
• XHR can’t do this
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method headers
body mode
crendentials cache
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headers
• POJSO(Plain Old JavaScript Object)
{
'Content-Type': 'text/plain',
'X-Custom-Header', 'ProcessThisImmediately'
}
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fetch('./api/some.json', {
method: 'POST',
mode: 'no-cors',
headers: {
'Content-Type': 'text/plain',
'X-Custom-Header', 'ProcessThisImmediately'
}
});
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What if
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What if
Header have multiple entry with the same name?
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Set-Cookie: JSESSIONID=alphabeta120394049; HttpOnly
Set-Cookie: AWSELBID=baaadbeef6767676767690220; Path=/alpha
https://community.apigee.com/articles/2319/how-to-handle-multi-value-headers-in-javascript.html
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RFC 2616
Multiple message-header fields with the same
field-name MAY be present in a message if and
only if the entire field-value for that header
field is defined as a comma-separated list
[i.e., #(values)]
http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2
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Header Class
• New global class
• For both request and response headers
https://developer.mozilla.org/en-US/docs/Web/API/Headers
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var h = new Headers();
h.append(
'Set-Cookie',
'JSESSIONID=alphabeta120394049; HttpOnly'
);
h.append(
'Set-Cookie',
'AWSELBID=baaadbeef6767676767690220; Path=/alpha'
);
fetch(url, {
headers: h
});
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var h = new Headers();
h.append(
'Set-Cookie',
'JSESSIONID=alphabeta120394049; HttpOnly'
);
h.append(
'Set-Cookie',
'AWSELBID=baaadbeef6767676767690220; Path=/alpha'
);
fetch(url, {
headers: h
});
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var h = new Headers();
h.append(
'Set-Cookie',
'JSESSIONID=alphabeta120394049; HttpOnly'
);
h.append(
'Set-Cookie',
'AWSELBID=baaadbeef6767676767690220; Path=/alpha'
);
fetch(url, {
headers: h
});
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append() delete()
get() getAll()
has() set()
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Deal with Response
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fetch('./api/some.json').then(function(response) {
return response.json();
})
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fetch('./api/some.json').then(function(response) {
return response.json();
})
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Response
• New global class
• Contains status, headers, body …
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ok status
url statusText
headers type
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ok status
url statusText
headers type
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ok
• “ok” is true when status is 2xx
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Means
• Fetch promise will resolve even when server
respond 404, 500 …
• Request is complete so Promise is resolved.
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Reject?
• On exception, ex: Network Error
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arrayBuffer() blob()
formData() json()
text() bodyUsed
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arrayBuffer() blob()
formData() json()
text() bodyUsed
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Response Body
• For formatted response body
• No auto format detection
• Body can consume only once
(save memory)
• Use clone when need consume twice
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fetch('...').then(function (res) {
if (res.ok) {
if (res.headers.get('Content-Type') === 'application/json')
return res.json();
}
}
})
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fetch('...').then(function (res) {
if (res.ok) {
if (res.headers.get('Content-Type') === 'application/json')
return res.json();
}
}
})
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fetch('...').then(function (res) {
if (res.ok) {
if (res.headers.get('Content-Type') === 'application/json')
return res.json();
}
}
})
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fetch('...').then(function (res) {
if (res.ok) {
if (res.headers.get('Content-Type') === 'application/json')
return res.json();
}
}
})
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New Classes
• Headers
• Response
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New Classes
• Headers
• Response
• Request
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Request
• Another new global class
• Contains method, headers, body …
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Where to Use
• Inside fetch
• As fetch input
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Ideally You Can
• Create a request object
• Reuse it
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var req = new Request('http://blah', {
method: 'POST',
body: requestBody
});
fetch(req);
fetch(req);
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But
• Body can only consumed once
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var req = new Request('http://blah', {
method: 'POST',
body: requestBody
});
fetch(req);
fetch(req); // TypeError
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Issue #61
• Fix the different behaviors
• Request will not able to reuse in the future
https://github.com/whatwg/fetch/issues/61
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Use fetch Now
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Polyfill
• by Github
https://github.com/github/fetch
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Node Polyfill
• node-fetch
https://www.npmjs.com/package/node-fetch
• isomorphic-fetch
https://www.npmjs.com/package/isomorphic-fetch
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Fact
• Debug:
Chrome, at ‘other tab’, request body not shows
Firefox, depend on response type
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Fact
• Safety flag for CORS not affect fetch
Affect Electron app
Use XHR + polyfill instead
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Fact
• Not able to cancel a fetch
• Issue #27
• No solution now
https://github.com/whatwg/fetch/issues/27
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Fact
• Not support progress now
• fetch-with-streams
• Future spec
https://github.com/yutakahirano/fetch-with-streams
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Streams
• WHATWG Spec
• Not Node Stream
• Base on Promise
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fetch(url).then(response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
function drain(valueSoFar) {
return reader.read().then(function(result) {
valueSoFar += decoder.decode(result.value || new Uint8Arr
if (result.done) return valueSoFar;
return drain(valueSoFar);
});
}
return drain();
}).then(function(fullText) {
console.log(fullText);
});
https://github.com/whatwg/fetch/issues/28#issuecomment-87209944
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fetch(url).then(response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
function drain(valueSoFar) {
return reader.read().then(function(result) {
valueSoFar += decoder.decode(result.value || new Uint8Arr
if (result.done) return valueSoFar;
return drain(valueSoFar);
});
}
return drain();
}).then(function(fullText) {
console.log(fullText);
});
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fetch(url).then(response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
function drain(valueSoFar) {
return reader.read().then(function(result) {
valueSoFar += decoder.decode(result.value || new Uint8Arr
if (result.done) return valueSoFar;
return drain(valueSoFar);
});
}
return drain();
}).then(function(fullText) {
console.log(fullText);
});
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fetch(url).then(response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
function drain(valueSoFar) {
return reader.read().then(function(result) {
valueSoFar += decoder.decode(result.value || new Uint8Arr
if (result.done) return valueSoFar;
return drain(valueSoFar);
});
}
return drain();
}).then(function(fullText) {
console.log(fullText);
});
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fetch(url).then(response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
function drain(valueSoFar) {
return reader.read().then(function(result) {
valueSoFar += decoder.decode(result.value || new Uint8Arr
if (result.done) return valueSoFar;
return drain(valueSoFar);
});
}
return drain();
}).then(function(fullText) {
console.log(fullText);
});
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fetch(url).then(response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
function drain(valueSoFar) {
return reader.read().then(function(result) {
valueSoFar += decoder.decode(result.value || new Uint8Arr
if (result.done) return valueSoFar;
return drain(valueSoFar);
});
}
return drain();
}).then(function(fullText) {
console.log(fullText);
});
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Code is complex
But when we use ES7
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Code is complex
But when we use ES7 async/await
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fetch(url).then(async response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
var fullText = '';
var result;
do {
result = await reader.read();
fullText += decoder.decode(result.value || new Uint8Array,
} while (!result.done);
console.log(fullText);
});
https://github.com/whatwg/fetch/issues/28#issuecomment-87209944
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fetch(url).then(async response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
var fullText = '';
var result;
do {
result = await reader.read();
fullText += decoder.decode(result.value || new Uint8Array,
} while (!result.done);
console.log(fullText);
});
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fetch(url).then(async response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
var fullText = '';
var result;
do {
result = await reader.read();
fullText += decoder.decode(result.value || new Uint8Array,
} while (!result.done);
console.log(fullText);
});
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fetch(url).then(async response => {
var reader = response.body.getReader();
var decoder = new TextDecoder();
var fullText = '';
var result;
do {
result = await reader.read();
fullText += decoder.decode(result.value || new Uint8Array,{
} while (!result.done);
console.log(fullText);
});
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Current Status
• Lots of new stuff is on the way
• Streams, cancel
• Browser integration
• Cache, HTTP/2, CSP, subresource integrity,
GET with body, busy indicator
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Summary
• fetch() supports lots of new stuff
• Simple API design
• Easy to use
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But
• fetch() is low level API
• Need write extra codes
• Hard to deal with general case
• So there is fetch-er
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fetch-er is the new $.ajax
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fetch-er
github.com/othree/fetcher
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fetch-er
• My open source project
• A fetch helper, like jQuery.ajax
• Named ‘fetch-er’
• NPM ‘fetcher’ already taken…
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Why
• fetch is low level API
• Already familiar with jQuery.ajax API
• Don’t repeat yourself
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Repeat?
• I must generate request body
• I must detect response type
• I must reject promise if response isn't ok
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fetcher.getJSON('/api/users').then(function (data) {
console.log(data[0]);
});
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fetcher.post('/api/users', {name: 'John'})
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fetcher.post('/api/users', {
name: 'John'
}, {
contentType: 'json'
})
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fetcher.method(url, data?, options?)
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Features
• Auto generate request body
• Auto parse response type and convert data
• jQuery similar behavior
• Timeout support
• Global options
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Dealing Response
• Always return an array
(Promise only accepts one value)
• [data, statusText, response]
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fetcher.get('/api/entry').then(function (res) {
var data = res[0];
var status = res[1];
var response = res[2];
});
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Why not use object?
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Why not use object?
Better for ES6 destructuring assign
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fetcher.get('/api/entry')
.then(function ([data, status, response]) {
});
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fetcher.get('/api/entry')
.then(([data, status, response]) => {
});
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Target User
• Want to use ES6 Promise to control flow
• Don’t want to deal with data formatting stuff
• Familiar with jQuery.ajax
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TODO
• jsonp?
• processData
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Patch Welcome
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One More Thing
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sendBeacon
• POST data to analytic service
• Don’t care about response
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navigator.sendBeacon('/log', analyticsData);
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Q?