<!DOCTYPE qhelp PUBLIC

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

"qhelp.dtd">

<qhelp>

<overview>

<p>

JavaScript allows local variables to be used before they are declared. However, this is confusing

for readers of the code, since it may not be clear whether the use refers to the local variable or

to a global variable of the same name.

</p>

</overview>

<recommendation>

<p>

Move local variable declarations to the beginning of the enclosing function, or (for global

variables) to the beginning of the source file.

</p>

</recommendation>

<example>

<p>

In the following example, the local variable <code>x</code> declared in function <code>f</code>

shadows the global variable of the same name. However, the first use of the local variable

precedes its declaration, so a developer unfamiliar with the code might assume that this use refers

to the global variable instead of the local variable.

</p>

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

</example>

<references>

<li>D. Crockford, <i>JavaScript: The Good Parts</i>, Section 4.9. O'Reilly, 2008.</li>

</references>

</qhelp>