MultipleArgumentsToSetConstructor.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>

<overview>
<p>
The <code>Set</code> constructor accepts an arbitrary number of arguments, but only the first one
is used to construct the set. The remaining arguments are ignored.
Code that invokes the <code>Set</code> constructor with multiple arguments is therefore likely to
be incorrect.
</p>
</overview>

<recommendation>
<p>
Only pass a single argument to the <code>Set</code> constructor, which should be an iterable object
(such as an array).
</p>
</recommendation>

<example>
<p>
The following example creates a set containing the vowels in the English language, and defines
a function that returns a boolean indicating whether a given character is a vowel:
</p>
<sample src="examples/MultipleArgumentsToSetConstructorBad.js"/>

<p>
However, this code does not work as intended: the <code>Set</code> constructor ignores all but
the first argument, so the <code>vowels</code> set only contains the letter <code>a</code>.
</p>

<p>
Instead, the list of vowels should be wrapped into an array:
</p>
<sample src="examples/MultipleArgumentsToSetConstructorGood.js"/>
</example>

<references>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/Set">MDN Web Docs: Set() constructor</a></li>
</references>
</qhelp>