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<title data-rh="true">Defer | foomo project docs</title><meta data-rh="true" name="viewport" content="width=device-width,initial-scale=1"><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:url" content="https://www.foomo.org/docs/backend/go-by-example/defer"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-default-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-rh="true" property="og:title" content="Defer | foomo project docs"><meta data-rh="true" name="description" content="In a normal Go application, control flows from the top to the bottom of any function that we call (this is if you don't use branching or looping)."><meta data-rh="true" property="og:description" content="In a normal Go application, control flows from the top to the bottom of any function that we call (this is if you don't use branching or looping)."><link data-rh="true" rel="icon" href="/img/favicon.ico"><link data-rh="true" rel="canonical" href="https://www.foomo.org/docs/backend/go-by-example/defer"><link data-rh="true" rel="alternate" href="https://www.foomo.org/docs/backend/go-by-example/defer" hreflang="en"><link data-rh="true" rel="alternate" href="https://www.foomo.org/docs/backend/go-by-example/defer" hreflang="x-default"><link data-rh="true" rel="preconnect" href="https://SUATUVZDDM-dsn.algolia.net" crossorigin="anonymous"><link rel="alternate" type="application/rss+xml" href="/blog/rss.xml" title="foomo project docs RSS Feed">
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fill="currentColor"></path></svg></a></li><li class="breadcrumbs__item"><span class="breadcrumbs__link">Go by example</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Defer</span><meta itemprop="position" content="2"></li></ul></nav><div class="theme-doc-markdown markdown"><h1>Defer</h1><p>In a normal Go application, control flows from the top to the bottom of any function that we call (this is if you don't use branching or looping).
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Through introducing <code>defer</code> we can execute the statement passed to it at the end of the function just before it returns. To demonstrate:</p><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">package</span><span class="token plain"> main</span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token keyword" style="font-style:italic">import</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">"fmt"</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token keyword" style="font-style:italic">func</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">main</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"first"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"second"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"third"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>If you copy the above code and execute it it will print 'first', 'second' and then 'third'. Now if we introduce <code>defer</code> to this function we see the order in which our statements are printed change.</p><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">func</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">main</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"first"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">defer</span><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"second"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"third"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>Executing this function will print: 'first', 'third' and then 'second'. This is because the statement that follows after the <code>defer</code> keyword is executed at the end of function we are calling, just before it returns.
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When it goes through this function if will print 'first', then it will recognise it has a defer function to call, it will print 'third' and then when it exits the function, it will check if there are any defer functions to call and if so it will call them.
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Which in our case is the print function that prints 'second'.
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What would happen if we add the defer keyword before each of our prints?</p><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">func</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">main</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">defer</span><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"first"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">defer</span><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"second"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">defer</span><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"third"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>This results into 'third' being printed first, followed by 'second' and then 'first'. This is because the defer keyword executes in last-in-first-out (LIFO) order.
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This makes sense because defer is usually used to close out resources, and it is logical to close these in the opposite order of which they are opened because one resource might be dependend on another one.</p><p>It's good practice to use defer to close a response body right after you have opened it. In this way you make sure all resources that have been opened have been closed and in this way it can prevent some bugs.
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What you will see often is something like this:</p><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">func</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">main</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> resp</span><span class="token punctuation" style="color:rgb(199, 146, 234)">,</span><span class="token plain"> err </span><span class="token operator" style="color:rgb(137, 221, 255)">:=</span><span class="token plain"> http</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Get</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token string" style="color:rgb(195, 232, 141)">"http://www.foomo.org"</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">if</span><span class="token plain"> err </span><span class="token operator" style="color:rgb(137, 221, 255)">!=</span><span class="token plain"> </span><span class="token boolean" style="color:rgb(255, 88, 116)">nil</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> log</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Fatal</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain">err</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">defer</span><span class="token plain"> resp</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token plain">Body</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Close</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>You open a resource, check if there is an error and after it use defer to close it before the function returns.</p><p>Another thing to keep in mind with defer is that it will execute with the value given to it at the time. To demonstrate:</p><div class="language-go codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-go codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">func</span><span class="token plain"> </span><span class="token function" style="color:rgb(130, 170, 255)">main</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> myVar </span><span class="token operator" style="color:rgb(137, 221, 255)">:=</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">"hello"</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token keyword" style="font-style:italic">defer</span><span class="token plain"> fmt</span><span class="token punctuation" style="color:rgb(199, 146, 234)">.</span><span class="token function" style="color:rgb(130, 170, 255)">Println</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain">myVar</span><span class="token punctuation" style="color:rgb(199, 146, 234)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> myVar </span><span class="token operator" style="color:rgb(137, 221, 255)">=</span><span class="token plain"> </span><span class="token string" style="color:rgb(195, 232, 141)">"goodbye"</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"></span><span class="token punctuation" style="color:rgb(199, 146, 234)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg viewBox="0 0 24 24" class="copyButtonIcon_y97N"><path fill="currentColor" d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg viewBox="0 0 24 24" class="copyButtonSuccessIcon_LjdS"><path fill="currentColor" d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>What do you think this prints? You might think it will print 'goodbye' because that is the last value of the variable before the main function returns.
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Surprisingly the value printed is 'hello', which is likely the result of a compiler optimization.</p></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-tags-row row margin-bottom--sm"><div class="col"><b>Tags:</b><ul class="tags_jXut padding--none margin-left--sm"><li class="tag_QGVx"><a class="tag_zVej tagRegular_sFm0" href="/docs/tags/go-basics">Go Basics</a></li></ul></div></div><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/foomo/foomo-docs/tree/main/foomo/docs/backend/go-by-example/defer.mdx" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/backend/setup"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">Setup</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/docs/backend/go-by-example/panic-and-recover"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">Panic and Recover</div></a></nav></div></div></div></div></main></div></div><footer class="footer"><div class="container container-fluid"><div class="row footer__links"><div class="col footer__col"><div class="footer__title">github</div><ul class="footer__items clean-list"><li class="footer__item"><a href="https://github.com/foomo" target="_blank" rel="noopener noreferrer" class="footer__link-item">https://github.com/foomo</a></li></ul></div><div class="col footer__col"><div class="footer__title">legal</div><ul class="footer__items clean-list"><li class="footer__item"><a class="footer__link-item" href="/etc/imprint">Imprint</a></li></ul></div></div><div class="footer__bottom text--center"><div class="footer__copyright">© 2023 bestbytes</div></div></div></footer></div>
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