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Author Topic: parseInt in JavaScript  (Read 4710 times)

Dakusan

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parseInt in JavaScript
« on: September 28, 2009, 05:31:49 AM »

Original post for parseInt in JavaScript can be found at https://www.castledragmire.com/Posts/parseInt_in_JavaScript.
Originally posted on: 08/27/08

A very important part of programming languages is the standard library that comes with them. PHP has one of the strongest base standard libraries I’ve ever seen. It’s also great to always be able to just throw out any function call in a script and not need look up the library file that you need to include! Perl has one of the largest official library sets (not included by standard) that I know if, but I find it a pain always having to remember which libraries I have to include for all the different functions I need. Though this is probably just because I don’t use Perl that much, as I have most of the C standard include libraries memorized, heh.

To properly use any function from any library, it is important to know exactly how it is supposed to work and any idiosyncrasies. You can never know EXACTLY how a function works unless you have the source for it, but you can pretty much always guess the gist of the internals.  This is one of the reasons I have always enjoyed writing my own Personal Libraries, besides that fact that I find it fun getting down in the nitty gritty of things.  Not knowing the inner workings of a function is not really a problem when programming, as this is the whole point of encapsulation, and documentation is usually sufficient enough.

I ran into a problem with the parseInt (sister of parseFloat) JavaScript function a long ways back however (this topic has been written down for years to talk about). JavaScript is kind of special in that it is a language that you just kind of jump into and assume you can quickly pick up everything, as there is very very little to its base library. One would assume that the “parseInt” function would just turn anything given to it into an integer, so “parseInt('123')” would return “123” and “parseInt(1.4)” would return “1”, as expected. The gotcha comes in if you pass a 0 before an integral number in a string, in which case it assumes the number is in octal (base 8 math). I found this out by accident when parsing time strings, where minutes are always 2 digits with leading 0s. When “parseInt('09')” is called, it returns “0” because 9 is not a part of base 8 math. Oops! parseInt stops at the first character it identifies that is not part of the base it is currently parsing in. Incidentally parseInt will also parse hex[adecimal] (base 16) strings, as per standard C syntax, for example, “parseInt('0x10')” returns “16”. I would have just said standard hex syntax, but not all languages represent hex in that manner, for example, Visual Basic requires &H before a hex number instead, like “&H10” represents “16”.

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