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Ensuring code quality</a></li><li><a href="/javascript/anti-patterns.html" class="sidebar-link">Anti-patterns</a></li><li><a href="/javascript/performance-tips.html" class="sidebar-link">Performance Tips</a></li><li><a href="/javascript/memory-efficiency.html" class="sidebar-link">Memory efficiency</a></li><li><a href="/javascript/reserved-keywords.html" class="sidebar-link">Reserved Keywords</a></li><li><a href="/javascript/contributors.html" class="sidebar-link">The Contributors</a></li></ul></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="fetch"><a href="#fetch" class="header-anchor">#</a> Fetch</h1> <h2 id="getting-json-data"><a href="#getting-json-data" class="header-anchor">#</a> Getting JSON data</h2> <div class="language-js extra-class"><pre class="language-js"><code><span class="token comment">// get some data from stackoverflow</span>
<span class="token function">fetch</span><span class="token punctuation">(</span><span class="token string">"https://api.stackexchange.com/2.2/questions/featured?order=desc&sort=activity&site=stackoverflow"</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span><span class="token parameter">resp</span> <span class="token operator">=></span> resp<span class="token punctuation">.</span><span class="token function">json</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span><span class="token parameter">json</span> <span class="token operator">=></span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>json<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">catch</span><span class="token punctuation">(</span><span class="token parameter">err</span> <span class="token operator">=></span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>err<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="set-request-headers"><a href="#set-request-headers" class="header-anchor">#</a> Set Request Headers</h2> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">fetch</span><span class="token punctuation">(</span><span class="token string">'/example.json'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
headers<span class="token operator">:</span> <span class="token keyword">new</span> <span class="token class-name">Headers</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
<span class="token string">'Accept'</span><span class="token operator">:</span> <span class="token string">'text/plain'</span><span class="token punctuation">,</span>
<span class="token string">'X-Your-Custom-Header'</span><span class="token operator">:</span> <span class="token string">'example value'</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="post-data"><a href="#post-data" class="header-anchor">#</a> POST Data</h2> <p>Posting form data</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">fetch</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">/example/submit</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
method<span class="token operator">:</span> <span class="token string">'POST'</span><span class="token punctuation">,</span>
body<span class="token operator">:</span> <span class="token keyword">new</span> <span class="token class-name">FormData</span><span class="token punctuation">(</span>document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">'example-form'</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>Posting JSON data</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">fetch</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">/example/submit.json</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
method<span class="token operator">:</span> <span class="token string">'POST'</span><span class="token punctuation">,</span>
body<span class="token operator">:</span> <span class="token constant">JSON</span><span class="token punctuation">.</span><span class="token function">stringify</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
email<span class="token operator">:</span> document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">'example-email'</span><span class="token punctuation">)</span><span class="token punctuation">.</span>value<span class="token punctuation">,</span>
comment<span class="token operator">:</span> document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">'example-comment'</span><span class="token punctuation">)</span><span class="token punctuation">.</span>value
<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="globalfetch"><a href="#globalfetch" class="header-anchor">#</a> GlobalFetch</h2> <p>The <a href="https://fetch.spec.whatwg.org/#globalfetch" target="_blank" rel="noopener noreferrer">GlobalFetch<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> interface exposes the <code>fetch</code> function, which can be used to request resources.</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">fetch</span><span class="token punctuation">(</span><span class="token string">'/path/to/resource.json'</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span><span class="token parameter">response</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>response<span class="token punctuation">.</span><span class="token function">ok</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">Error</span><span class="token punctuation">(</span><span class="token string">"Request failed!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> response<span class="token punctuation">.</span><span class="token function">json</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span><span class="token parameter">json</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>json<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>The resolved value is a <a href="https://fetch.spec.whatwg.org/#response-class" target="_blank" rel="noopener noreferrer">Response<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> Object. This Object contains the body of the response, as well as it's status and headers.</p> <h2 id="send-cookies"><a href="#send-cookies" class="header-anchor">#</a> Send cookies</h2> <p>The fetch function does not send cookies by default. There are two possible ways to send cookies:</p> <ol><li>Only send cookies if the URL is on the same origin as the calling script.</li></ol> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">fetch</span><span class="token punctuation">(</span><span class="token string">'/login'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
credentials<span class="token operator">:</span> <span class="token string">'same-origin'</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre></div><ol><li>Always send cookies, even for cross-origin calls.</li></ol> <div class="language-js extra-class"><pre class="language-js"><code><span class="token function">fetch</span><span class="token punctuation">(</span><span class="token string">'https://otherdomain.com/login'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
credentials<span class="token operator">:</span> <span class="token string">'include'</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre></div><h2 id="using-fetch-to-display-questions-from-the-stack-overflow-api"><a href="#using-fetch-to-display-questions-from-the-stack-overflow-api" class="header-anchor">#</a> Using Fetch to Display Questions from the Stack Overflow API</h2> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> url <span class="token operator">=</span>
<span class="token string">'http://api.stackexchange.com/2.2/questions?site=stackoverflow&tagged=javascript'</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> questionList <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">'ul'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
document<span class="token punctuation">.</span>body<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>questionList<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> responseData <span class="token operator">=</span> <span class="token function">fetch</span><span class="token punctuation">(</span>url<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span><span class="token parameter">response</span> <span class="token operator">=></span> response<span class="token punctuation">.</span><span class="token function">json</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
responseData<span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter"><span class="token punctuation">{</span>items<span class="token punctuation">,</span> has_more<span class="token punctuation">,</span> quota_max<span class="token punctuation">,</span> quota_remaining<span class="token punctuation">}</span></span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">const</span> <span class="token punctuation">{</span>title<span class="token punctuation">,</span> score<span class="token punctuation">,</span> owner<span class="token punctuation">,</span> link<span class="token punctuation">,</span> answer_count<span class="token punctuation">}</span> <span class="token keyword">of</span> items<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">const</span> listItem <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">'li'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
questionList<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>listItem<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> a <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">'a'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
listItem<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>a<span class="token punctuation">)</span><span class="token punctuation">;</span>
a<span class="token punctuation">.</span>href <span class="token operator">=</span> link<span class="token punctuation">;</span>
a<span class="token punctuation">.</span>textContent <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">[</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>score<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">] </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>title<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> (by </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>owner<span class="token punctuation">.</span>display_name <span class="token operator">||</span> <span class="token string">'somebody'</span><span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">)</span><span class="token template-punctuation string">`</span></span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h4 id="syntax"><a href="#syntax" class="header-anchor">#</a> Syntax</h4> <ul><li>promise = fetch(url).then(function(response) {})</li> <li>promise = fetch(url, options)</li> <li>promise = fetch(request)</li></ul> <h4 id="parameters"><a href="#parameters" class="header-anchor">#</a> Parameters</h4> <table><thead><tr><th>Options</th> <th>Details</th></tr></thead> <tbody><tr><td><code>method</code></td> <td>The HTTP method to use for the request. ex: <code>GET</code>, <code>POST</code>, <code>PUT</code>, <code>DELETE</code>, <code>HEAD</code>. Defaults to <code>GET</code>.</td></tr> <tr><td><code>headers</code></td> <td>A <code>Headers</code> object containing additional HTTP headers to include in the request.</td></tr> <tr><td><code>body</code></td> <td>The request payload, can be a <code>string</code> or a <code>FormData</code> object. Defaults to <code>undefined</code></td></tr> <tr><td><code>cache</code></td> <td>The caching mode. <code>default</code>, <code>reload</code>, <code>no-cache</code></td></tr> <tr><td><code>referrer</code></td> <td>The referrer of the request.</td></tr> <tr><td><code>mode</code></td> <td><code>cors</code>, <code>no-cors</code>, <code>same-origin</code>. Defaults to <code>no-cors</code>.</td></tr> <tr><td><code>credentials</code></td> <td><code>omit</code>, <code>same-origin</code>, <code>include</code>. Defaults to <code>omit</code>.</td></tr> <tr><td><code>redirect</code></td> <td><code>follow</code>, <code>error</code>, <code>manual</code>. Defaults to <code>follow</code>.</td></tr> <tr><td><code>integrity</code></td> <td>Associated integrity metadata. Defaults to empty string.</td></tr></tbody></table> <h4 id="remarks"><a href="#remarks" class="header-anchor">#</a> Remarks</h4> <p><a href="https://fetch.spec.whatwg.org" target="_blank" rel="noopener noreferrer">The Fetch standard<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> defines requests, responses, and the process that binds them: fetching.</p> <p>Among other interfaces, the standard defines <code>Request</code> and <code>Response</code> Objects, designed to be used for all operations involving network requests.</p> <p>A useful application of these interfaces is <code>GlobalFetch</code>, which can be used to load remote resources.</p> <p>For browsers that do not yet support the Fetch standard, GitHub has a <a href="https://github.com/github/fetch" target="_blank" rel="noopener noreferrer">polyfill<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> available. In addition, there is also a <a href="https://github.com/bitinn/node-fetch" target="_blank" rel="noopener noreferrer">Node.js implementation<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> that is useful for server/client consistency.</p> <p>In the absence of cancelable Promises you can't abort the fetch request (<a href="https://github.com/whatwg/fetch/issues/27" target="_blank" rel="noopener noreferrer">github issue<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>). But there is a <a href="https://github.com/domenic/cancelable-promise" target="_blank" rel="noopener noreferrer">proposal<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> by the T39 in stage 1 for cancelable promises.</p></div> <footer class="page-edit"><div class="edit-link"><a href="https://github.com/devtut/generate/edit/master/docs/javascript/fetch.md" target="_blank" rel="noopener noreferrer">Edit this page on GitHub</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev">
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