<!DOCTYPE qhelp PUBLIC

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

"qhelp.dtd">

<qhelp>

<overview>

<p>

Assigning a variable to itself typically indicates a mistake such as a missing

<code>this</code> qualifier or a misspelled variable name.

</p>

</overview>

<recommendation>

<p>

Carefully inspect the assignment to check for misspellings or missing qualifiers.

</p>

<p>

If the self-assignment is intentional and is needed for documentation or optimization purposes,

add a JSDoc comment with a <tt>@type</tt> tag. This will indicate the self-assignment is intentional.

</p>

</recommendation>

<example>

<p>

In the example below, the constructor function <code>Rectangle</code> is intended

to initialize properties <code>x</code>, <code>y</code>, <code>width</code>, and

<code>height</code> to the parameters of the same names.

</p>

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

<p>

Note, however, that on line 4 the programmer forgot to qualify the left hand side of

the assignment with <code>this</code>: the code now performs a useless assignment of

the <code>width</code> parameter to itself and leaves the <code>width</code>

property uninitialized.

</p>

<p>

To fix this issue, insert a <code>this</code> qualifier:

</p>

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

</example>

<references>

<li>Ecma International, <i>ECMAScript Language Definition</i>, 5.1 Edition, Section 11.13. ECMA, 2011.</li>

</references>

</qhelp>