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» Best Practices
<a
target="_blank"
href="https://github.com/pmd/pmd/blob/main/docs/../pmd-javascript/src/main/resources/category/ecmascript/bestpractices.xml"
class="float-right"
role="button"
><i class="fab fa-github fa-lg"></i> Edit on GitHub</a
>
</div>
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</header>
<div class="post-header">
<h1 class="post-title-main">Best Practices</h1>
</div>
<div class="post-content" data-github-edit-url="https://github.com/pmd/pmd/blob/main/docs/../pmd-javascript/src/main/resources/category/ecmascript/bestpractices.xml">
<div class="summary">Rules which enforce generally accepted best practices.</div>
<details id="inline-toc-details">
<summary>Table of Contents</summary>
<div id="inline-toc"><!-- empty, move TOC here when screen size too small --></div>
</details>
<!-- DO NOT EDIT THIS FILE. This file is generated from file ../pmd-javascript/src/main/resources/category/ecmascript/bestpractices.xml. -->
<h2 id="avoidwithstatement">AvoidWithStatement</h2>
<p><strong>Since:</strong> PMD 5.0.1</p>
<p><strong>Priority:</strong> High (1)</p>
<p>Avoid using with - it’s bad news</p>
<p><strong>This rule is defined by the following XPath expression:</strong></p>
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">WithStatement</span><span class="w">
</span></code></pre></div></div>
<p><strong>Example(s):</strong></p>
<div class="language-javascript highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">with</span> <span class="p">(</span><span class="nx">object</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">property</span> <span class="o">=</span> <span class="mi">3</span><span class="p">;</span> <span class="c1">// Might be on object, might be on window: who knows.</span>
<span class="p">}</span>
</code></pre></div></div>
<p><strong>Use this rule by referencing it:</strong></p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"category/ecmascript/bestpractices.xml/AvoidWithStatement"</span> <span class="nt">/&gt;</span>
</code></pre></div></div>
<h2 id="consistentreturn">ConsistentReturn</h2>
<p><strong>Since:</strong> PMD 5.0</p>
<p><strong>Priority:</strong> Medium High (2)</p>
<p>ECMAScript does provide for return types on functions, and therefore there is no solid rule as to their usage.
However, when a function does use returns they should all have a value, or all with no value. Mixed return
usage is likely a bug, or at best poor style.</p>
<p><strong>This rule is defined by the following Java class:</strong> <a href="https://github.com/pmd/pmd/blob/main/pmd-javascript/src/main/java/net/sourceforge/pmd/lang/ecmascript/rule/bestpractices/ConsistentReturnRule.java">net.sourceforge.pmd.lang.ecmascript.rule.bestpractices.ConsistentReturnRule</a></p>
<p><strong>Example(s):</strong></p>
<div class="language-javascript highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// Ok</span>
<span class="kd">function</span> <span class="nx">foo</span><span class="p">()</span> <span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="nx">condition1</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span> <span class="kc">true</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">return</span> <span class="kc">false</span><span class="p">;</span>
<span class="p">}</span>
<span class="c1">// Bad</span>
<span class="kd">function</span> <span class="nx">bar</span><span class="p">()</span> <span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="nx">condition1</span><span class="p">)</span> <span class="p">{</span>
<span class="k">return</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">return</span> <span class="kc">false</span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div></div>
<p><strong>Use this rule by referencing it:</strong></p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"category/ecmascript/bestpractices.xml/ConsistentReturn"</span> <span class="nt">/&gt;</span>
</code></pre></div></div>
<h2 id="globalvariable">GlobalVariable</h2>
<p><strong>Since:</strong> PMD 5.0</p>
<p><strong>Priority:</strong> High (1)</p>
<p>This rule helps to avoid using accidently global variables by simply missing the "var" declaration.
Global variables can lead to side-effects that are hard to debug.</p>
<p><strong>This rule is defined by the following XPath expression:</strong></p>
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">Assignment</span><span class="p">[</span><span class="nt">Name</span><span class="err">/</span><span class="na">@GlobalName</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="nf">true</span><span class="p">()]</span><span class="w">
</span></code></pre></div></div>
<p><strong>Example(s):</strong></p>
<div class="language-javascript highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">function</span><span class="p">(</span><span class="nx">arg</span><span class="p">)</span> <span class="p">{</span>
<span class="nx">notDeclaredVariable</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span> <span class="c1">// this will create a global variable and trigger the rule</span>
<span class="kd">var</span> <span class="nx">someVar</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span> <span class="c1">// this is a local variable, that's ok</span>
<span class="nb">window</span><span class="p">.</span><span class="nx">otherGlobal</span> <span class="o">=</span> <span class="mi">2</span><span class="p">;</span> <span class="c1">// this will not trigger the rule, although it is a global variable.</span>
<span class="p">}</span>
</code></pre></div></div>
<p><strong>Use this rule by referencing it:</strong></p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"category/ecmascript/bestpractices.xml/GlobalVariable"</span> <span class="nt">/&gt;</span>
</code></pre></div></div>
<h2 id="scopeforinvariable">ScopeForInVariable</h2>
<p><strong>Since:</strong> PMD 5.0</p>
<p><strong>Priority:</strong> High (1)</p>
<p>A for-in loop in which the variable name is not explicitly scoped to the enclosing scope with the ‘var’ keyword can
refer to a variable in an enclosing scope outside the nearest enclosing scope. This will overwrite the
existing value of the variable in the outer scope when the body of the for-in is evaluated. When the for-in loop
has finished, the variable will contain the last value used in the for-in, and the original value from before
the for-in loop will be gone. Since the for-in variable name is most likely intended to be a temporary name, it
is better to explicitly scope the variable name to the nearest enclosing scope with ‘var’.</p>
<p><strong>This rule is defined by the following XPath expression:</strong></p>
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">ForInLoop</span><span class="p">[</span><span class="ow">not</span><span class="p">(</span><span class="kn">child::</span><span class="nt">VariableDeclaration</span><span class="p">)]</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="m">1</span><span class="p">]</span><span class="w">
</span></code></pre></div></div>
<p><strong>Example(s):</strong></p>
<div class="language-javascript highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// Ok</span>
<span class="kd">function</span> <span class="nx">foo</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">p</span> <span class="o">=</span> <span class="dl">'</span><span class="s1">clean</span><span class="dl">'</span><span class="p">;</span>
<span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">obj</span> <span class="o">=</span> <span class="p">{</span> <span class="na">dirty</span><span class="p">:</span> <span class="dl">'</span><span class="s1">dirty</span><span class="dl">'</span> <span class="p">};</span>
<span class="k">for</span> <span class="p">(</span><span class="kd">var</span> <span class="nx">p</span> <span class="k">in</span> <span class="nx">obj</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Use 'var' here.</span>
<span class="nx">obj</span><span class="p">[</span><span class="nx">p</span><span class="p">]</span> <span class="o">=</span> <span class="nx">obj</span><span class="p">[</span><span class="nx">p</span><span class="p">];</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">x</span><span class="p">;</span>
<span class="p">}();</span>
<span class="c1">// 'p' still has value of 'clean'.</span>
<span class="p">}</span>
<span class="c1">// Bad</span>
<span class="kd">function</span> <span class="nx">bar</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">p</span> <span class="o">=</span> <span class="dl">'</span><span class="s1">clean</span><span class="dl">'</span><span class="p">;</span>
<span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">obj</span> <span class="o">=</span> <span class="p">{</span> <span class="na">dirty</span><span class="p">:</span> <span class="dl">'</span><span class="s1">dirty</span><span class="dl">'</span> <span class="p">};</span>
<span class="k">for</span> <span class="p">(</span><span class="nx">p</span> <span class="k">in</span> <span class="nx">obj</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// Oh no, missing 'var' here!</span>
<span class="nx">obj</span><span class="p">[</span><span class="nx">p</span><span class="p">]</span> <span class="o">=</span> <span class="nx">obj</span><span class="p">[</span><span class="nx">p</span><span class="p">];</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">x</span><span class="p">;</span>
<span class="p">}();</span>
<span class="c1">// 'p' is trashed and has value of 'dirty'!</span>
<span class="p">}</span>
</code></pre></div></div>
<p><strong>Use this rule by referencing it:</strong></p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"category/ecmascript/bestpractices.xml/ScopeForInVariable"</span> <span class="nt">/&gt;</span>
</code></pre></div></div>
<h2 id="usebasewithparseint">UseBaseWithParseInt</h2>
<p><strong>Since:</strong> PMD 5.0.1</p>
<p><strong>Priority:</strong> High (1)</p>
<p>This rule checks for usages of parseInt. While the second parameter is optional and usually defaults
to 10 (base/radix is 10 for a decimal number), different implementations may behave differently.
It also improves readability, if the base is given.</p>
<p>See also: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt">parseInt()</a></p>
<p><strong>This rule is defined by the following XPath expression:</strong></p>
<div class="language-xpath highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="o">//</span><span class="nt">FunctionCall</span><span class="o">/</span><span class="nt">Name</span><span class="p">[</span><span class="w">
</span><span class="na">@Identifier</span><span class="w"> </span><span class="err">=</span><span class="w"> </span><span class="s1">'parseInt'</span><span class="w">
</span><span class="ow">and</span><span class="w">
</span><span class="nf">count</span><span class="p">(..</span><span class="err">/*</span><span class="p">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="m">3</span><span class="w">
</span><span class="p">]</span><span class="w">
</span></code></pre></div></div>
<p><strong>Example(s):</strong></p>
<div class="language-javascript highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nb">parseInt</span><span class="p">(</span><span class="dl">"</span><span class="s2">010</span><span class="dl">"</span><span class="p">);</span> <span class="c1">// unclear, could be interpreted as 10 or 7 (with a base of 7)</span>
<span class="nb">parseInt</span><span class="p">(</span><span class="dl">"</span><span class="s2">10</span><span class="dl">"</span><span class="p">,</span> <span class="mi">10</span><span class="p">);</span> <span class="c1">// good</span>
</code></pre></div></div>
<p><strong>Use this rule by referencing it:</strong></p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">ref=</span><span class="s">"category/ecmascript/bestpractices.xml/UseBaseWithParseInt"</span> <span class="nt">/&gt;</span>
</code></pre></div></div>
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