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.


You might find this post useful; it points out some of the differences between closures in Javascript and Perl.

Two undefs , use === !== operators as per this (Page 109)

Regarding the similarities rather than the differences, I've made this list of Perl and JavaScript equivalents, which I often refer to when I've forgotten how to do something in JavaScript.

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About Steven Haryanto

user-pic A programmer (mostly Perl 5 nowadays).