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<h1 class="article-title" itemprop="name">Parse Parameters</h1>
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<a target="_blank" rel="noopener external nofollow noreferrer" href="https://github.com/harttle/liquidjs/edit/master/docs/source/tutorials/parse-parameters.md" class="article-edit-link" title="Improve this doc"><i class="icon-pencil"></i></a>
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<h2 id="Access-Raw-Parameters" class="article-heading"><a href="#Access-Raw-Parameters" class="headerlink" title="Access Raw Parameters"></a>Access Raw Parameters<a class="article-anchor" href="#Access-Raw-Parameters" aria-hidden="true"></a></h2><p>As covered in <a href="/tutorials/register-filters-tags.html">Register Filters/Tags</a>, tag parameters is available on <code>tagToken.args</code> as a raw string. For example:</p>
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<figure class="highlight javascript"><table><tr><td class="code"><pre><span class="line"><span class="comment">// Usage: {% random foo bar coo %}</span></span><br><span class="line"><span class="comment">// Output: "foo", "bar" or "coo"</span></span><br><span class="line">engine.registerTag(<span class="string">'random'</span>, {</span><br><span class="line"> <span class="function"><span class="title">parse</span>(<span class="params">tagToken</span>)</span> {</span><br><span class="line"> <span class="comment">// tagToken.args === "foo bar coo"</span></span><br><span class="line"> <span class="built_in">this</span>.items = tagToken.args.split(<span class="string">' '</span>)</span><br><span class="line"> },</span><br><span class="line"> <span class="function"><span class="title">render</span>(<span class="params">context, emitter</span>)</span> {</span><br><span class="line"> <span class="comment">// get a random index</span></span><br><span class="line"> <span class="keyword">const</span> index = <span class="built_in">Math</span>.floor(<span class="built_in">this</span>.items.length * <span class="built_in">Math</span>.random())</span><br><span class="line"> <span class="comment">// output that item</span></span><br><span class="line"> emitter.write(<span class="built_in">this</span>.items[index])</span><br><span class="line"> }</span><br><span class="line">})</span><br></pre></td></tr></table></figure>
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<p>Here’s a JSFiddle version: <a target="_blank" rel="noopener external nofollow noreferrer" href="http://jsfiddle.net/ctj364up/2/">http://jsfiddle.net/ctj364up/2/</a></p>
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<h2 id="Parse-Parameters-as-Values" class="article-heading"><a href="#Parse-Parameters-as-Values" class="headerlink" title="Parse Parameters as Values"></a>Parse Parameters as Values<a class="article-anchor" href="#Parse-Parameters-as-Values" aria-hidden="true"></a></h2><p>Sometimes we need more dynamic tags and want to pass values to the custom tag instead of static strings. Variables in LiquidJS can be literal (string, number, etc.) or a variable from current context scope.</p>
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<p>The following modified template also contains 3 values to random from, but they’re values instead of static strings. The first one is string literal, second one is an identifier, third one is a property access sequence containing two identifiers.</p>
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<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">{% random "foo" bar obj.coo %}</span><br></pre></td></tr></table></figure>
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<p>It can be tricky to parse all these cases manually, but there’s a <a href="/api/classes/parser_tokenizer_.tokenizer.html">Tokenizer</a> class in LiquidJS you can make use of.</p>
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<figure class="highlight javascript"><table><tr><td class="code"><pre><span class="line"><span class="keyword">const</span> { Liquid, Tokenizer, evalToken } = <span class="built_in">require</span>(<span class="string">'liquidjs'</span>)</span><br><span class="line">engine.registerTag(<span class="string">'random'</span>, {</span><br><span class="line"> <span class="function"><span class="title">parse</span>(<span class="params">tagToken</span>)</span> {</span><br><span class="line"> <span class="keyword">const</span> tokenizer = <span class="keyword">new</span> Tokenizer(tagToken.args)</span><br><span class="line"> <span class="built_in">this</span>.items = []</span><br><span class="line"> <span class="keyword">while</span> (!tokenizer.end()) {</span><br><span class="line"> <span class="comment">// here readValue() returns a LiteralToken or PropertyAccessToken</span></span><br><span class="line"> <span class="built_in">this</span>.items.push(tokenizer.readValue())</span><br><span class="line"> }</span><br><span class="line"> },</span><br><span class="line"> * <span class="function"><span class="title">render</span>(<span class="params">context, emitter</span>)</span> {</span><br><span class="line"> <span class="keyword">const</span> index = <span class="built_in">Math</span>.floor(<span class="built_in">this</span>.items.length * <span class="built_in">Math</span>.random())</span><br><span class="line"> <span class="keyword">const</span> token = <span class="built_in">this</span>.items[index]</span><br><span class="line"> <span class="comment">// in LiquidJS, we use yield to wait for async call</span></span><br><span class="line"> <span class="keyword">const</span> value = <span class="keyword">yield</span> evalToken(token, context)</span><br><span class="line"> emitter.write(value)</span><br><span class="line"> }</span><br><span class="line">})</span><br></pre></td></tr></table></figure>
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<p>Calling this tag in scope <code>{ bar: "bar", obj: { coo: "coo" } }</code> yields exactly the same result as the first example. See this JSFiddle: <a target="_blank" rel="noopener external nofollow noreferrer" href="http://jsfiddle.net/ctj364up/3/">http://jsfiddle.net/ctj364up/3/</a></p>
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<blockquote class="note info"><strong class="note-title">Async ans Promises</strong><p>Async calls in LiquidJS are implemented by generators directly, for we can call generators in synchronous manner so this tag implementation is also valid for <code>renderSync()</code>, <code>parseAndRenderSync()</code>, <code>renderFileSync()</code>. If you need to await a promise in tag implementation, simply replace <code>await somePromise</code> with <code>yield somePromise</code> and keep <code>* render()</code> instead of <code>async render()</code> will do the trick. See <a href="/tutorials/sync-and-async.html">Sync and Async</a> for more details.</p>
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<h2 id="Parse-Key-Value-Pairs-as-Named-Parameters" class="article-heading"><a href="#Parse-Key-Value-Pairs-as-Named-Parameters" class="headerlink" title="Parse Key-Value Pairs as Named Parameters"></a>Parse Key-Value Pairs as Named Parameters<a class="article-anchor" href="#Parse-Key-Value-Pairs-as-Named-Parameters" aria-hidden="true"></a></h2><p>Named parameters become very handy when there’re optional parameters or lots of parameters, in which case the order of parameters is not important. This is exactly what <a href="/api/classes/template_tag_hash_.hash.html">Hash</a> class is invented for.</p>
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<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">{% random from:2, to:max %}</span><br></pre></td></tr></table></figure>
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<p>In the above example, we’re trying to generate a random number in the range [2, max]. We’ll use <code>Hash</code> to parse <code>from</code> and <code>to</code> parameters.</p>
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<figure class="highlight javascript"><table><tr><td class="code"><pre><span class="line"><span class="keyword">const</span> { Liquid, Hash } = <span class="built_in">require</span>(<span class="string">'liquidjs'</span>)</span><br><span class="line"></span><br><span class="line">engine.registerTag(<span class="string">'random'</span>, {</span><br><span class="line"> <span class="function"><span class="title">parse</span>(<span class="params">tagToken</span>)</span> {</span><br><span class="line"> <span class="comment">// parse the parameters structure into `this.args`</span></span><br><span class="line"> <span class="built_in">this</span>.args = <span class="keyword">new</span> Hash(tagToken.args)</span><br><span class="line"> },</span><br><span class="line"> * <span class="function"><span class="title">render</span>(<span class="params">context, emitter</span>)</span> {</span><br><span class="line"> <span class="comment">// evaluate the parameters in `context`</span></span><br><span class="line"> <span class="keyword">const</span> {<span class="keyword">from</span>, to} = <span class="keyword">yield</span> <span class="built_in">this</span>.args.render(context)</span><br><span class="line"> <span class="keyword">const</span> length = to - <span class="keyword">from</span> + <span class="number">1</span></span><br><span class="line"> <span class="keyword">const</span> value = <span class="keyword">from</span> + <span class="built_in">Math</span>.floor(length * <span class="built_in">Math</span>.random())</span><br><span class="line"> emitter.write(value)</span><br><span class="line"> }</span><br><span class="line">})</span><br></pre></td></tr></table></figure>
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<p>Rendering <code>{% random from:2, to:max %}</code> in scope <code>{ max: 10 }</code> will generate a random number in the range [2, 10]. See this JSFiddle: <a target="_blank" rel="noopener external nofollow noreferrer" href="http://jsfiddle.net/ctj364up/4/">http://jsfiddle.net/ctj364up/4/</a></p>
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<time class="article-footer-updated" datetime="2022-01-22T15:25:05.203Z" itemprop="dateModified">Last updated: 2022-01-22</time>
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<a href="access-scope-in-filters.html" class="article-footer-prev" title="Access Scope in Filters"><i class="icon-chevron-left"></i><span>Prev</span></a><a href="sync-and-async.html" class="article-footer-next" title="Sync and Async"><span>Next</span><i class="icon-chevron-right"></i></a>
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<ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#Access-Raw-Parameters"><span class="toc-text">Access Raw Parameters</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Parse-Parameters-as-Values"><span class="toc-text">Parse Parameters as Values</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Parse-Key-Value-Pairs-as-Named-Parameters"><span class="toc-text">Parse Key-Value Pairs as Named Parameters</span></a></li></ol>
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