Rabu, 23 Juni 2010

Perl vs JavaScript

Here are some notes I made while hacking on Language::Expr::Compiler::JS. Of course, there are a million differences between the two, but these focus mostly on operators and types. Hope it can be useful.

  • Double vs single quotes. There are practically no functional differences between double-quoted string and single-quoted one in JavaScript. In Perl, single quotes do not interpret escape sequences other than \\ and \', but in JavaScript both single- and double-quoted strings interpret the same set of escape sequences.

  • String escape sequences. Perl does not support JavaScript's \v (vertical tab), while JavaScript does not support \N{NAME} (named Unicode character), \e and \c[ (escape/control), \a (alarm bell).

  • Two undefs. JavaScript has two special nothingness/undefinedness: null and undefined. Strangely, null == undefined and they are equal to themselves, but they are not equal to any other values (including 0, '', false). The difference between the two is just this: undefined is not a keyword but a global variable (you can assign to it, but of course you shouldn't). If you want less confusion, just use null.

  • Behaviour of "+". Since JavaScript only has "+" (while Perl has "+" and "."), you should be aware that "+" in JavaScript coerces to strings when one of the operands is a string (e.g. 1 + "2" becomes "12"). In Perl, "+" coerces to numbers. So be careful when mixing numbers and strings.

  • You need to explicitly "return" value from a function. But there's a cute shortcut for one statement functions introduced in JavaScript 1.8: 'function (x) x*3' which is equivalent to 'function (x) { return x*3 }' so in this case you don't need the "return".

  • Boolean. JavaScript has real boolean. In Perl you can use 'boolean' from CPAN which gives you practically the same stuff.

  • JavaScript lacks a lot of Perl convenience operators, including <=> cmp, low-precedenced and/or/not, //, =~, ~~, qq(), qx(), qw(), m//, s///, **, etc.



All in all, I think JavaScript is quite nice and simple language with familiar syntax (at least compared to PHP). It also has lexical variables, anonymous functions, OO, etc.

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