<p>The most useful, high-level part of the Fetch API is the <code>fetch()</code> function. In its simplest form it takes a URL and returns a promise that resolves to the response. The response is captured as a <code>Response</code> object.</p>
<p>The <code>fetch()</code> function’s arguments are the same as those passed to the <br/><code>Request()</code> constructor, so you may directly pass arbitrarily complex requests to <code>fetch()</code> as discussed below.</p>
<h2>Headers</h2>
<p>Fetch introduces 3 interfaces. These are <code>Headers</code>, <code>Request</code> and <br/><code>Response</code>. They map directly to the underlying HTTP concepts, but have <br/>certain visibility filters in place for privacy and security reasons, such as <br/>supporting CORS rules and ensuring cookies aren’t readable by third parties.</p>
<p>The <ahref="https://fetch.spec.whatwg.org/#headers-class">Headers interface</a> is a simple multi-map of names to values:</p>
<p>Some of these operations are only useful in ServiceWorkers, but they provide <br/>a much nicer API to Headers.</p>
<p>Since Headers can be sent in requests, or received in responses, and have various limitations about what information can and should be mutable, <code>Headers</code> objects have a <strong>guard</strong> property. This is not exposed to the Web, but it affects which mutation operations are allowed on the Headers object. <br/>Possible values are:</p>
<p>The details of how each guard affects the behaviors of the Headers object are <br/>in the <ahref="https://fetch.spec.whatwg.org/">specification</a>. For example, you may not append or set a “request” guarded Headers’ “Content-Length” header. Similarly, inserting “Set-Cookie” into a Response header is not allowed so that ServiceWorkers may not set cookies via synthesized Responses.</p>
<p>All of the Headers methods throw TypeError if <code>name</code> is not a <ahref="https://fetch.spec.whatwg.org/#concept-header-name">valid HTTP Header name</a>. The mutation operations will throw TypeError if there is an immutable guard. Otherwise they fail silently. For example:</p>
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<pre><span>var</span> res <span>=</span> Response.<span>error</span><span>(</span><span>)</span><span>;</span>
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<pre><span>var</span> res <span>=</span> Response.<span>error</span><span>(</span><span>)</span><span>;</span>
console.<span>log</span><span>(</span><span>"Cannot pretend to be a bank!"</span><span>)</span><span>;</span>
<span>}</span></pre></td>
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<span>}</span></pre></div>
</div>
<h2>Request</h2>
<p>The Request interface defines a request to fetch a resource over HTTP. URL, method and headers are expected, but the Request also allows specifying a body, a request mode, credentials and cache hints.</p>
<p>The simplest Request is of course, just a URL, as you may do to GET a resource.</p>
<p>You may also pass a Request to the <code>Request()</code> constructor to create a copy. <br/>(This is not the same as calling the <code>clone()</code> method, which is covered in <br/>the “Reading bodies” section.).</p>
<p>Again, this form is probably only useful in ServiceWorkers.</p>
<p>The non-URL attributes of the <code>Request</code> can only be set by passing initial <br/>values as a second argument to the constructor. This argument is a dictionary.</p>
<p>The Request’s mode is used to determine if cross-origin requests lead to valid responses, and which properties on the response are readable. Legal mode values are <code>"same-origin"</code>, <code>"no-cors"</code> (default) and <code>"cors"</code>.</p>
<p>The <code>"same-origin"</code> mode is simple, if a request is made to another origin with this mode set, the result is simply an error. You could use this to ensure that <br/>a request is always being made to your origin.</p>
<p>The <code>"no-cors"</code> mode captures what the web platform does by default for scripts you import from CDNs, images hosted on other domains, and so on. First, it prevents the method from being anything other than “HEAD”, “GET” or “POST”. Second, if any ServiceWorkers intercept these requests, they may not add or override any headers except for <ahref="https://fetch.spec.whatwg.org/#simple-header">these</a>. Third, JavaScript may not access any properties of the resulting Response. This ensures that ServiceWorkers do not affect the semantics of the Web and prevents security and privacy issues that could arise from leaking data across domains.</p>
<p><code>"cors"</code> mode is what you’ll usually use to make known cross-origin requests to access various APIs offered by other vendors. These are expected to adhere to <br/>the <ahref="https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS">CORS protocol</a>. Only a <ahref="https://fetch.spec.whatwg.org/#concept-filtered-response-cors">limited set</a> of headers is exposed in the Response, but the body is readable. For example, you could get a list of Flickr’s <ahref="https://www.flickr.com/services/api/flickr.interestingness.getList.html">most interesting</a> photos today like this:</p>
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<pre><span>var</span> u <span>=</span><span>new</span> URLSearchParams<span>(</span><span>)</span><span>;</span>
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<pre><span>var</span> u <span>=</span><span>new</span> URLSearchParams<span>(</span><span>)</span><span>;</span>
<p>The <code>credentials</code> enumeration determines if cookies for the other domain are <br/>sent to cross-origin requests. This is similar to XHR’s <code>withCredentials</code><br/>flag, but tri-valued as <code>"omit"</code> (default), <code>"same-origin"</code> and <code>"include"</code>.</p>
<p>The Request object will also give the ability to offer caching hints to the user-agent. This is currently undergoing some <ahref="https://github.com/slightlyoff/ServiceWorker/issues/585">security review</a>. Firefox exposes the attribute, but it has no effect.</p>
<p>The “error” type results in the <code>fetch()</code> Promise rejecting with TypeError.</p>
<p>There are certain attributes that are useful only in a ServiceWorker scope. The <br/>idiomatic way to return a Response to an intercepted request in ServiceWorkers is:</p>
<p>As you can see, Response has a two argument constructor, where both arguments are optional. The first argument is a body initializer, and the second is a dictionary to set the <code>status</code>, <code>statusText</code> and <code>headers</code>.</p>
<p>The static method <code>Response.error()</code> simply returns an error response. Similarly, <code>Response.redirect(url, status)</code> returns a Response resulting in <br/>a redirect to <code>url</code>.</p>
<p>This is a significant improvement over XHR in terms of ease of use of non-text data!</p>
<p>Request bodies can be set by passing <code>body</code> parameters:</p>
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<pre><span>var</span> form <span>=</span><span>new</span> FormData<span>(</span>document.<span>getElementById</span><span>(</span><span>'login-form'</span><span>)</span><span>)</span><span>;</span>
<div>
<pre><span>var</span> form <span>=</span><span>new</span> FormData<span>(</span>document.<span>getElementById</span><span>(</span><span>'login-form'</span><span>)</span><span>)</span><span>;</span>
<p>Responses take the first argument as the body.</p>
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<pre><span>var</span> res <span>=</span><span>new</span> Response<span>(</span><span>new</span> File<span>(</span><span>[</span><span>"chunk"</span><span>,</span><span>"chunk"</span><span>]</span><span>,</span><span>"archive.zip"</span><span>,</span>
<pre><span>var</span> res <span>=</span><span>new</span> Response<span>(</span><span>new</span> File<span>(</span><span>[</span><span>"chunk"</span><span>,</span><span>"chunk"</span><span>]</span><span>,</span><span>"archive.zip"</span><span>,</span>
<p>Both Request and Response (and by extension the <code>fetch()</code> function), will try to intelligently <ahref="https://fetch.spec.whatwg.org/#concept-bodyinit-extract">determine the content type</a>. Request will also automatically set a “Content-Type” header if none is set in the dictionary.</p>
<h3>Streams and cloning</h3>
<p>It is important to realise that Request and Response bodies can only be read once! Both interfaces have a boolean attribute <code>bodyUsed</code> to determine if it is safe to read or not.</p>
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<pre><span>var</span> res <span>=</span><span>new</span> Response<span>(</span><span>"one time use"</span><span>)</span><span>;</span>
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<pre><span>var</span> res <span>=</span><span>new</span> Response<span>(</span><span>"one time use"</span><span>)</span><span>;</span>
<p>This decision allows easing the transition to an eventual <ahref="https://streams.spec.whatwg.org/">stream-based</a> Fetch API. The intention is to let applications consume data as it arrives, allowing for JavaScript to deal with larger files like videos, and perform things like compression and editing on the fly.</p>
<p>Often, you’ll want access to the body multiple times. For example, you can use the upcoming <ahref="http://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cache-objects">Cache API</a> to store Requests and Responses for offline use, and Cache requires bodies to be available for reading.</p>
<p>So how do you read out the body multiple times within such constraints? The API provides a <code>clone()</code> method on the two interfaces. This will return a clone of the object, with a ‘new’ body. <code>clone()</code> MUST be called before the body of the corresponding object has been used. That is, <code>clone()</code> first, read later.</p>
<p>Along with the transition to streams, Fetch will eventually have the ability to abort running <code>fetch()</code>es and some way to report the progress of a fetch. These are provided by XHR, but are a little tricky to fit in the Promise-based nature of the Fetch API.</p>
<h3>Prepared by <ahref="http://www.vcu.edu/engweb">Ann
" height="38 " width="38 "/></a></h2>
<h3>Prepared by <ahref="http://www.vcu.edu/engweb">Ann
Woodlief,</a> Virginia Commonwealth University</h3>
<h5>Click on text in red for hypertext notes and questions</h5> I am a rather elderly man. The nature of my avocations for the last thirty years has brought me into more than ordinary contact with what would seem an interesting and somewhat singular set of men of whom as yet nothing that I know of has ever been written:-- I mean the law-copyists or scriveners. I have known very many of them, professionally and privately, and if I pleased, could relate divers histories, at which good-natured gentlemen might smile, and sentimental souls might weep. But I waive the biographies of all other scriveners for a few passages in the life of Bartleby, who was a scrivener the strangest I ever saw or heard of. While of other law-copyists I might write the complete life, of Bartleby nothing of that sort can be done. I believe that no materials exist for a full and satisfactory biography of this man. It is an irreparable loss to literature. Bartleby was one of those beings of whom nothing is ascertainable, except from the original sources, and in his case those are very small. What my own astonished eyes saw of Bartleby, that is all I know of him, except, indeed, one vague report which will appear in the sequel.
<p>Ere introducing the scrivener, as he first appeared to me, it is fit I make some mention of myself, my employees, my business, my chambers, and general surroundings; because some such description is indispensable to an adequate understanding of the chief character about to be presented. </p>
@ -258,6 +256,6 @@
<p>* * * * * * * *</p>
<p>There would seem little need for proceeding further in this history. Imagination will readily supply the meagre recital of poor Bartleby's interment. But ere parting with the reader, let me say, that if this little narrative has sufficiently interested him, to awaken curiosity as to who Bartleby was, and what manner of life he led prior to the present narrator's making his acquaintance, I can only reply, that in such curiosity I fully share, but am wholly unable to gratify it. Yet here I hardly know whether I should divulge one little item of rumor, which came to my ear a few months after the scrivener's decease. Upon what basis it rested, I could never ascertain; and hence how true it is I cannot now tell. But inasmuch as this vague report has not been without a certain strange suggestive interest to me, however said, it may prove the same with some others; and so I will briefly mention it. The report was this: that Bartleby had been a subordinate clerk in the Dead Letter Office at <ahref="http://raven.cc.ukans.edu/%7Ezeke/bartleby/parker.html"target="_blank">Washington</a>, from which he had been suddenly removed by a change in the administration. When I think over this rumor, I cannot adequately express the emotions which seize me. Dead letters! does it not sound like dead men? Conceive a man by nature and misfortune prone to a pallid hopelessness, can any business seem more fitted to heighten it than that of continually handling these dead letters and assorting them for the flames? For by the cart-load they are annually burned. Sometimes from out the folded paper the pale clerk takes a ring:--the bank-note sent in swiftest charity:--he whom it would relieve, nor eats nor hungers any more; pardon for those who died despairing; hope for those who died unhoping; good tidings for those who died stifled by unrelieved calamities. On errands of life, these letters speed to death. </p>
<p>Through our pursuit of further automation and maximization of margins during the industrial age of media technology, we built advertising technology to optimize publishers’ yield of marketing budgets that had eroded after the last recession. Looking back now, our scraping of dimes may have cost us dollars in consumer loyalty. The fast, scalable systems of targeting users with ever-heftier advertisements have slowed down the public internet and drained more than a few batteries. We were so clever and so good at it that we over-engineered the capabilities of the plumbing laid down by, well, ourselves. This steamrolled the users, depleted their devices, and tried their patience.</p>
<p>The rise of ad blocking poses a threat to the internet and could potentially drive users to an enclosed platform world dominated by a few companies. We have let the fine equilibrium of content, commerce, and technology get out of balance in the open web. We had, and still do have, a responsibility to educate the business side, and in some cases to push back. We lost sight of our social and ethical responsibility to provide a safe, usable experience for anyone and everyone wanting to consume the content of their choice.</p>
<p>We need to bring that back into alignment, starting right now.</p>
<p>
<ahref="http://www.iab.com/wp-content/uploads/2015/10/getting-lean-with-digital-ad-ux.jpg"><imgwidth="300"height="250"alt="Getting LEAN with Digital Ad UX"src="http://www.iab.com/wp-content/uploads/2015/10/getting-lean-with-digital-ad-ux-300x250.jpg"/></a>Today, the IAB Tech Lab is launching the L.E.A.N. Ads program. Supported by the Executive Committee of the IAB Tech Lab Board, IABs around the world, and hundreds of member companies, L.E.A.N. stands for Light, Encrypted, Ad choice supported, Non-invasive ads. These are principles that will help guide the next phases of advertising technical standards for the global digital advertising supply chain.</p>
<p><ahref="http://www.iab.com/wp-content/uploads/2015/10/getting-lean-with-digital-ad-ux.jpg"><imgwidth="300"height="250"alt="Getting LEAN with Digital Ad UX"src="http://www.iab.com/wp-content/uploads/2015/10/getting-lean-with-digital-ad-ux-300x250.jpg"/></a>Today, the IAB Tech Lab is launching the L.E.A.N. Ads program. Supported by the Executive Committee of the IAB Tech Lab Board, IABs around the world, and hundreds of member companies, L.E.A.N. stands for Light, Encrypted, Ad choice supported, Non-invasive ads. These are principles that will help guide the next phases of advertising technical standards for the global digital advertising supply chain.</p>
<p>As with any other industry, standards should be created by non-profit standards-setting bodies, with many diverse voices providing input. We will invite all parties for public comment, and make sure consumer interest groups have the opportunity to provide input.</p>
<p>L.E.A.N. Ads do not replace the current advertising standards many consumers still enjoy and engage with while consuming content on our sites across all IP enabled devices. Rather, these principles will guide an alternative set of standards that provide choice for marketers, content providers, and consumers.</p>
<p>Among the many areas of concentration, we must also address frequency capping on retargeting in Ad Tech and make sure a user is targeted appropriately before, but never AFTER they make a purchase. If we are so good at reach and scale, we can be just as good, if not better, at moderation. Additionally, we must address volume of ads per page as well as continue on the path to viewability. The dependencies here are critical to an optimized user experience.</p>
@ -19,14 +18,18 @@
<p>The IAB Tech Lab will continue to provide the tools for publishers in the digital supply chain to have a dialogue with users about their choices so that content providers can generate revenue while creating value. Publishers should have the opportunity to provide rich advertising experiences, L.E.A.N. advertising experiences, and subscription services. Or publishers can simply deny their service to users who choose to keep on blocking ads. That is all part of elasticity of consumer tolerance and choice.</p>
<p>Finally, we must do this in an increasingly fragmented market, across screens. We must do this in environments where entire sites are blocked, purposefully or not. Yes, it is disappointing that our development efforts will have to manage with multiple frameworks while we work to supply the economic engine to sustain an open internet. However, our goal is still to provide diverse content and voices to as many connected users as possible around the world.</p>
<p>That is user experience.</p>
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<td>IAB Tech Lab Members can join the IAB Tech Lab Ad Blocking Working Group, please email <ahref="mailto:adblocking@iab.com">adblocking@iab.com</a> for more information.</td>
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<p>IAB Tech Lab Members can join the IAB Tech Lab Ad Blocking Working Group, please email <ahref="mailto:adblocking@iab.com">adblocking@iab.com</a> for more information.</p>
<p>Read <atarget="_blank"href="http://www.iab.com/insights/ad-blocking/">more about ad blocking here</a>.</p>
<li> "It's your fault for using Red Hat! You should be using Debian/<wbr/>Mandrake/<wbr/>Gentoo instead!" </li>
<li> "Red Hat 7.2 is totally obsolete! It's almost 14 months old! What were you expecting!" </li>
</ul>
</td>
<td>
<p> While I am flattered that so many logorrheic Linux fanboys are sufficiently interested in my opinions and experiences to share their deeply heartfelt views with me, you can all rest assured that: </p>
<ul>
<ultype="A">
@ -49,7 +51,7 @@ RPMs</a>, and it sucks about the same as mplayer, and in about the same ways, th
<p> Then I checked out <ahref="http://www.dtek.chalmers.se/groups/dvd/">Ogle</a> again, and it hasn't been updated since the last time I tried, six months ago. It's a pretty decent DVD player, if you have the physical DVD. It does on-screen menus, and you can click on them with the mouse. But I don't need a DVD player (I have a hardware DVD player that works just fine.) It can't, as far as I can tell, play anything but actual discs. </p>
<p> Oh, and even though I have libdvdcss installed (as evidenced by the fact that Ogle actually works) Xine won't play the same disc that Ogle will play. It seems to be claiming that the CSS stuff isn't installed, which it clearly is. </p>
<p> An idiocy that all of these programs have in common is that, in addition to opening a window for the movie, and a window for the control panel, they <i>also</i> spray a constant spatter of curses crud on the terminal they were started from. I imagine at some point, there was some user who said, ``this program is pretty nice, but you know what it's missing? It's missing a lot of pointless chatter about what plugins and fonts have been loaded!'' </p>
<hr/><b>And here's the Random Commentary section:</b>
<hr/><b>And here's the Random Commentary section:</b>
Whenever a programmer thinks, "Hey, skins, what a cool idea", their
@ -84,4 +86,4 @@ RPMs</a>, and it sucks about the same as mplayer, and in about the same ways, th
</blockquote>
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<p><ahref="http://fakehost/"><imgalt="[ up ]"src="http://fakehost/compass1.gif"onmouseover="this.src="../compass2.gif""onmouseout="this.src="../compass1.gif""/></a></p>
<li> "Red Hat 7.2 is totally obsolete! It's almost 14 months old! What were you expecting!" </li>
</ul>
</td>
<tdbgcolor="#FEFFE6">
<p> While I am flattered that so many logorrheic Linux fanboys are sufficiently interested in my opinions and experiences to share their deeply heartfelt views with me, you can all rest assured that: </p>
David A Roberts
6 years ago
committed by
Gijs