<!DOCTYPE qhelp PUBLIC

"-//Semmle//qhelp//EN"

"qhelp.dtd">

<qhelp>

<overview>

<p>

In JavaScript, cases in a switch statement can have arbitrary expressions as their labels.

The interpreter does not check that these expressions are all different. At runtime,

if two cases in a switch statement have the same label, the second case will never be

executed. This most likely indicates a copy-paste error where the first case was copied

and then not properly adjusted.

</p>

</overview>

<recommendation>

<p>

Examine the two cases to find out what they were meant to check. If both the case labels

and their statements are identical, then the second case is duplicate code

that can be deleted. Otherwise, the second case label needs to be adjusted.

</p>

</recommendation>

<example>

<p>

In the example below, the function <code>controller</code> checks its parameter <code>msg</code>

to determine what operation it is meant to perform. Note that the 'switch' statement has two

cases labeled <code>'start'</code>; the second one will never be executed.

</p>

<sample src="examples/DuplicateSwitchCase.js" />

<p>

Clearly, the second case should be labeled <code>'stop'</code>:

</p>

<sample src="examples/DuplicateSwitchCaseGood.js" />

</example>

</qhelp>