TemporalDeadZone.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>
<overview>
<p>
The scope of a variable declared with <code>let</code> is its innermost enclosing block statement, loop or
function. Unlike variables declared with <code>var</code>, variables declared with <code>let</code> are not
hoisted to the top of their scope, giving rise to a region of code where the variable is in scope, but not
declared yet. Accessing a <code>let</code>-bound variable inside this so-called "temporal dead zone"
is permitted by some legacy implementations, but is illegal in ECMAScript 2015.
</p>

</overview>
<recommendation>

<p>
Move the <code>let</code> declaration to the beginning of its scope.
</p>

</recommendation>
<example>

<p>
In the following example, <code>x</code> is initialized before its declaration:
</p>

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

<p>
The declaration should be moved as follows:
</p>

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

</example>
<references>
<li>Mozilla Developer Network: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#Temporal_dead_zone_and_errors_with_let">Temporal dead zone and errors with let</a>.</li>
</references>
</qhelp>