The parseInt() function parses a string and returns an integer.
The radix parameter is used to specify which numeral system to be used, for example, a radix of 16 (hexadecimal) indicates that the number in the string should be parsed from a hexadecimal number to a decimal number.
If the radix parameter is omitted, JavaScript assumes the following:
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If the string begins with "0x", the radix is 16 (hexadecimal)
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If the string begins with "0", the radix is 8 (octal). This feature is deprecated
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If the string begins with any other value, the radix is 10 (decimal)
[http://www.w3schools.com/jsref/jsref_parseInt.asp]