Equivalents in JavaScript and Perl

This page is a list of similarities between Perl and JavaScript to help go from one language to the other.

Bold face indicates an argument or optional element. The × symbol means that something is not available. For example, JavaScript has no equivalent to Perl's quotemeta.

The links on Perl keywords go to perldoc.perl.org. Most of the JavaScript keywords are linked to w3schools.com, but where that site doesn't cover something, the links go to the Mozilla Developers' Network page.

Strings

uc $str

str.toUpperCase ()

lc $str

str.toLowerCase ()

ucfirst $str
lcfirst $str

JavaScript has no equivalent single functions for these.

int $str

parseInt (str)

hex $str

parseInt(str,16) parseInt('0x'+str)

Convert a string to a number as if the string is hexadecimal.

ord $str

str.charCodeAt(0)

ord (substr $str, $n, 1)

str.charCodeAt(n)

chr $number

String.fromCharCode(number)

In the JavaScript, the "String" is part of the function call, like the "Math" in "Math.sin". It is not a variable.

sprintf ("%X", $number)

number.toString (16)

Make hexadecimal strings from a number.

split str/regex $str

str.split (str/regex)

substr $string, offset, length

str.substr (offset, length)
str.substring (start, end)

index $str, something

str.indexOf (something)

index ($str, something, -1)
rindex ($str, something)

str.lastIndexOf(something)

Find the last occurence of something in str

length $str

str.length

Length of a string

$str =~ tr/abc/xyz/

Perl's "tr" has no equivalent in JavaScript.

. (Concatenation operator)

+
concat

String concatenation is via "." in Perl, but "+" in JavaScript. JavaScript also uses "+" for addition of numbers.

sprintf, printf

JavaScript has no equivalent.

$str x $n

str.repeat(n)

substr ($str, $n, 1)

str.charAt(n)

$str =~ /\Q$end$/

str.endsWith(end)

Perl does not have an equivalent function.

$str =~ /^\Q$begin\E/

str.startsWith(begin)

Perl does not have an equivalent function.

$str =~ /\Q$included\E/

str.includes(included)

Perl does not have an equivalent function.

$str =~ s/^\s+|\s+$//g

str.trim ()

Perl does not have an equivalent function, although it is found in several modules, such as Data::Munge.

Regexes

$str =~ s/regex/y/

str.replace (/regex/, y)

$str =~ s/regex/function ($1, $2)/e

str.replace (/regex/, function (match, first, second) { code } )

The JavaScript "replace" can take a function as the second argument. This function takes the matched text as its argument, followed by the match of each pair of brackets (like Perl's $1, $2, etc.) and its return value is inserted into the string. See ECMAScript specification 15.5.4.11.

$str =~ m/regex/

str.match (/regex/)
regex.test (str)

$str =~ s/regex/y/g

str.replace (/regex/g, y)

quotemeta

JavaScript does not have an equivalent.

pos str

regex.lastIndex ()

In JavaScript, the position is associated with a regex rather than a string.

Hashes / objects

my %hash

var hash=new Object()

JavaScript's objects function as hashes.

my %hash = (a => "b", c => "d")

var hash = {"a" : "b", "c" : "d"}

$hash{key}

hash[key]
hash.key

Access hash keys using the [ ] or . notation in JavaScript.

@all_keys = keys %hash

all_keys = Object.keys (hash)

Object.values appeared first in ECMAScript version 5.1. See the next entry for how to loop over keys of a hash in JavaScript.

for my $i (keys %hash) { }

for (var i in hash)

These loop over all the keys in a hash (associative array).

values (%hash)

Object.values (hash)

Object.values appeared first in ECMAScript 2017 Draft. It is currently "experimental".

defined $variable

typeof (variable) != "undefined"

delete $hash{key}

delete hash[key]

exists

JavaScript has no equivalent.

Arrays

my @arr = ()

var arr = new Array ()

my @arr = ('hot', 'cold')

var arr = new Array ("hot", "cold")

@arr = qw/cat fish dog/

arr = "cat fish dog".split (/\s+/)

pop @arr

arr.pop

Most of JavaScript's array operators seem to have been based on Perl and have the same names.

push @arr, $value

arr.push (value)

push @arr, @otherarr

arr.push (otherarr)

@finalarr = (@arr, @otherarr)

finalarr = arr.concat (otherarr)

Perl doesn't have a special function for this.

reverse @arr

arr.reverse

splice @arr, offset, length

arr.splice (offset, length)

sort @arr

arr.sort

sort {some code} @arr

arr.sort (some function)

These sort using a user-defined method of comparing.

join str, @arr

arr.join (str)

These join the elements of an array together.

scalar @arr
$#arr + 1

arr.length

These functions give the number of elements in an array

map

Until ECMA version 5, this used to have no equivalent in JavaScript. The JavaScript library jQuery supplies an equivalent to Perl's map.

grep

This has no equivalent in JavaScript. The JavaScript library jQuery supplies an equivalent to Perl's grep.

JavaScript has repeat for strings.

"@array"

array.toString ()

Perl does not have an explicit equivalent (convert any object into a string). However, arrays, strings, and numbers are automatically converted into strings in a print context.

Specific functions

sin, cos, exp, etc.

Math.sin, Math.cos, Math.exp, etc.

Both JavaScript and Perl use the same names for their mathematical functions as C. JavaScript puts "Math." before each function name.

$x**$y

Math.pow(x, y)

rand

Math.random ()

Unlike most of the maths functions, neither of these is like the C functions rand or random. They both return a number between 0 and 1.

sprintf ("%.0f", $_), POSIX round

Math.round ()

Perl doesn't have a standard way of rounding numbers.

link, socket, mkdir, and anything else to do with files, sockets, processes, etc.

Originally JavaScript did not have equivalents because JavaScript was only meant to run inside a web browser.

warn

alert

print "Answer: ";
$str = <STDIN>;
$str = "default" unless $str;

str = prompt ("Answer: ", "default");

The Perl example is a command-line equivalent.

URI::Escape uri_escape

escape
encodeURI

Perl does not have a built-in equivalent.

URI::Escape uri_unescape

unescape
decodeURI

MIME::Base64 encode_base64

btoa

atob and btoa are not part of any JavaScript standard. They will work on most implementations except older versions of Internet Explorer.

MIME::Base64 decode_base64

atob

ualarm (from core module Time::HiRes)

setTimeout

Program control

exit

throw (exception)

JavaScript has no function to halt execution.

die

throw (exception)

continue

JavaScript uses the same names as C, C++, and Java for loop control.

JavaScript has no equivalent.

eval { code }

try/catch

eval $str

eval

goto

JavaScript has no "goto".

return

sub

function

Perl does not have "functions", and JavaScript does not have subroutines, although each of these commands does both jobs.

caller

function.caller.toString()
arguments.callee.caller.toString()

function is the name of the current function.

bless

new

In Perl, bless is called to register an object's type after it has been created. Perl modules often have a "new" function, but this is not part of Perl - the "new" function could be called anything. "bless", however, is part of Perl.

Module::function ($object)

function.call (object)

Here function is the name of the function and Module is the name of the Perl module. $object in Perl is an instance of Module.

switch

There is no switch in Perl.

Variables and values

var, let

JavaScript now also includes "let" for defining variables. "let" is much closer to Perl's "my" than "var", which has lots of weird properties.

use constant c => 1

const c = 1;

undef, 0, an empty string

false

Perl does not have booleans

Any value except 0, a string of length zero, or the special value undef.

true

JavaScript has no equivalent to Perl's $_.

$a, $b

JavaScript has no equivalent to Perl's $a and $b. A function argument to sort is assumed to have two arguments.

@ARGV

JavaScript has no equivalent to Perl's @ARGV.

arguments

JavaScript's "arguments" also functions similarly to Perl's caller.

$1, $2, $3, etc.

$x = qr/regex/

x = new RegExp (regex)

(reference operator)

JavaScript has no equivalent.

'Inf', '-Inf'

Infinity, -Infinity

See Special floating point: infinity (Inf) and not-a-number (NaN) in perldata.

'NaN'

NaN

Dynamic document creation

open

doc=Window.open
doc.open

doc.close

document.write
console.log

Writes to the current document in JavaScript, to STDOUT (the default filehandle) in Perl. console.log writes to the console in JavaScript.

print FH

doc.write

Print to a particular document doc in JavaScript, a particular file handle FH in Perl.

say

document.writeln

In Perl 5.10, "say" is the same as "print" except that it appends a new line character after what it has printed. JavaScript's "writeln" and "write" have the same relationship.

Equivalents in JavaScript and Perl

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