Eval() function in javascript

[seowebtrick]

i want to use that eval() on my website, please tell me the correct because this is not working.

<script type="text/javascript">
eval("x=10;y=20;document.write(x*y)");
document.write("<br />" + eval("2+2"));
document.write("<br />" + eval(x+17));
</script>


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