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"></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></a></div></div></div></header><div class="css-xbsqlp css-15lkjjo"><div class="css-1m1176 css-95xunl"><div class="css-12vsfho"><div class="css-tctv7l"><div class="css-10335ra"><article class="css-174qq1k"><header class="css-hgc6lu"><h1 class="css-1obw60b">New in React v0.4: Autobind by Default</h1></header><div class="css-acl5jg">July 02, 2013 <span class="css-1glzrmu">by <a href="https://twitter.com/zpao" class="css-1hs4uiz">Paul O’Shannessy</a></span></div><div class="css-124oy3v"><div class="css-6nf64v"><div class="scary"> <blockquote> <p>This blog site has been archived. Go to <a href="https://react.dev/blog" target="_blank" rel="nofollow noopener noreferrer">react.dev/blog</a> to see the recent posts.</p> </blockquote> </div> <p>React v0.4 is very close to completion. As we finish it off, we’d like to share with you some of the major changes we’ve made since v0.3. This is the first of several posts we’ll be making over the next week.</p> <h2 id="what-is-reactautobind"><a href="#what-is-reactautobind" aria-hidden class="anchor"><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>What is React.autoBind? </h2> <p>If you take a look at most of our current examples, you’ll see us using <code class="gatsby-code-text">React.autoBind</code> for event handlers. This is used in place of <code class="gatsby-code-text">Function.prototype.bind</code>. Remember that in JS, <a href="https://bonsaiden.github.io/JavaScript-Garden/#function.this" target="_blank" rel="nofollow noopener noreferrer">function calls are late-bound</a>. That means that if you simply pass a function around, the <code class="gatsby-code-text">this</code> used inside won’t necessarily be the <code class="gatsby-code-text">this</code> you expect. <code class="gatsby-code-text">Function.prototype.bind</code> creates a new, properly bound, function so that when called, <code class="gatsby-code-text">this</code> is exactly what you expect it to be.</p> <p>Before we launched React, we would write this:</p> <div class="gatsby-highlight has-highlighted-lines" data-language="jsx"><pre class="gatsby-code-jsx"><code class="gatsby-code-jsx">React<span class="token punctuation">.</span><span class="token function">createClass</span><span class="token punctuation">(</span><span class="token punctuation">{</span> <span class="token function-variable function">onClick</span><span class="token operator">:</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">event</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token comment">/* do something with this */</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token function-variable function">render</span><span class="token operator">:</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="gatsby-highlight-code-line"> <span class="token keyword">return</span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>button</span> <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">onClick</span><span class="token punctuation">.</span><span class="token function">bind</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">}</span></span> <span class="token punctuation">/></span></span><span class="token punctuation">;</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> <p>We wrote <code class="gatsby-code-text">React.autoBind</code> as a way to cache the function creation and save on memory usage. Since <code class="gatsby-code-text">render</code> can get called multiple times, if you used <code class="gatsby-code-text">this.onClick.bind(this)</code> you would actually create a new function on each pass. With React v0.3 you were able to write this instead:</p> <div class="gatsby-highlight has-highlighted-lines" data-language="jsx"><pre class="gatsby-code-jsx"><code class="gatsby-code-jsx">React<span class="token punctuation">.</span><span class="token function">createClass</span><span class="token punctuation">(</span><span class="token punctuation">{</span> <span class="gatsby-highlight-code-line"> <span class="token literal-property property">onClick</span><span class="token operator">:</span> React<span class="token punctuation">.</span><span class="token function">autoBind</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">event</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token comment">/* do something with this */</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">,</span></span> <span class="token function-variable function">render</span><span class="token operator">:</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="gatsby-highlight-code-line"> <span class="token keyword">return</span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>button</span> <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>onClick<span class="token punctuation">}</span></span> <span class="token punctuation">/></span></span><span class="token punctuation">;</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> <h2 id="whats-changing-in-v04"><a href="#whats-changing-in-v04" aria-hidden class="anchor"><svg aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>What’s Changing in v0.4? </h2> <p>After using <code class="gatsby-code-text">React.autoBind</code> for a few weeks, we realized that there were very few times that we didn’t want that behavior. So we made it the default! Now all methods defined within <code class="gatsby-code-text">React.createClass</code> will already be bound to the correct instance.</p> <p>Starting with v0.4 you can just write this:</p> <div class="gatsby-highlight has-highlighted-lines" data-language="jsx"><pre class="gatsby-code-jsx"><code class="gatsby-code-jsx">React<span class="token punctuation">.</span><span class="token function">createClass</span><span class="token punctuation">(</span><span class="token punctuation">{</span> <span class="gatsby-highlight-code-line"> <span class="token function-variable function">onClick</span><span class="token operator">:</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">event</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token comment">/* do something with this */</span><span class="token punctuation">}</span><span class="token punctuation">,</span></span> <span class="token function-variable function">render</span><span class="token operator">:</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="gatsby-highlight-code-line"> <span class="token keyword">return</span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>button</span> <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>onClick<span class="token punctuation">}</span></span> <span class="token punctuation">/></span></span><span class="token punctuation">;</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> <p>For v0.4 we will simply be making <code class="gatsby-code-text">React.autoBind</code> a no-op — it will just return the function you pass to it. Most likely you won’t have to change your code to account for this change, though we encourage you to update. We’ll publish a migration guide documenting this and other changes that come along with React v0.4.</p></div><div class="css-1m173d1"><span class="css-11xil2b"><span>Is this page useful?<button aria-label="Yes" class="css-1k9fay3"><svg focusable="false" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 81.13 89.76" class="css-15scox9"><path d="M22.9 6a18.57 18.57 0 002.67 8.4 25.72 25.72 0 008.65 7.66c3.86 2 8.67 7.13 13.51 11 3.86 3.11 8.57 7.11 11.54 8.45s13.59.26 14.64 1.17c1.88 1.63 1.55 9-.11 15.25-1.61 5.86-5.96 10.55-6.48 16.86-.4 4.83-2.7 4.88-10.93 4.88h-1.35c-3.82 0-8.24 2.93-12.92 3.62a68 68 0 01-9.73.5c-3.57 0-7.86-.08-13.25-.08-3.56 0-4.71-1.83-4.71-4.48h8.42a3.51 3.51 0 000-7H12.28a2.89 2.89 0 01-2.88-2.88 1.91 1.91 0 01.77-1.78h16.46a3.51 3.51 0 000-7H12.29c-3.21 0-4.84-1.83-4.84-4a6.41 6.41 0 011.17-3.78h19.06a3.5 3.5 0 100-7H9.75A3.51 3.51 0 016 42.27a3.45 3.45 0 013.75-3.48h13.11c5.61 0 7.71-3 5.71-5.52-4.43-4.74-10.84-12.62-11-18.71-.15-6.51 2.6-7.83 5.36-8.56m0-6a6.18 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