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copied!<ul> <li>In V8 <code>null</code>, <code>undefined</code>, <code>true</code> and <code>false</code> internally are <a href="https://github.com/v8/v8/blob/c736a452575f406c9a05a8c202b0708cb60d43e5/src/objects.h#L9368" rel="nofollow noreferrer">heap allocated objects</a>. If you are comming from Java you can say that <code>true</code> and <code>false</code> in V8 are more like <code>Boolean.TRUE</code> and <code>Boolean.FALSE</code> in Java.</li> <li>There is an important difference between <em>real</em> local variables and variables that are captured by closures or shadowed by eval/with. Captures variables are stored in a special heap allocated structure called <a href="http://code.google.com/p/v8/source/browse/trunk/src/contexts.h?r=12394#165" rel="nofollow noreferrer">Context</a> and are accessed indirectly. For more details about <em>real</em> vs. context allocates variables see <a href="https://stackoverflow.com/questions/5326300/garbage-collection-with-node-js/5328761#5328761">my answer to a different question</a></li> <li><p>V8 has two compilers: non-optimizing (aka full) and optimizing one:</p> <ul> <li>Non-optimizing compiler can't store floating point numbers and integers beyond 31-bit (32-bit on x64) on the stack it always boxes them into <a href="http://code.google.com/p/v8/source/browse/trunk/src/objects.h?r=12408#1297" rel="nofollow noreferrer">HeapNumber</a>s. It does not try to do register allocation and stores <em>real</em> local variables on the stack.</li> <li>Optimizing compiler is much smarter. It does register allocation (linear scan) and can keep full 32-bit integers and floating point numbers on the stack and in the registers (including XMM registers).</li> </ul></li> <li><p>Speaking of JVM: it can perform so called <em>stack allocation</em> and allocate a non-escaping object on the stack instead of the heap. A more generic optimization (<em>scalar replacement</em>) can sometimes completely eliminate allocation of non-escaping object and explode it into separate fields.</p></li> </ul>

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