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The second argument (10) specifies you want to use a base 10 numbering system. It's unusual to use anything for this parameter except 10 and you should always specify it as the default is a bit unpredictable. (See, for example, http://www.w3schools.com/jsref/jsref_obj_global.asp
if you are interested as to why.)
If you need to have decimals then use parseFloat(). For example this script returns floating point values 1234.345 and 34.7 respectively into X:
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