mod

Andrew.


Influenced by Perl: JavaScript function storage

I’m interested in various language paradigms, syntax, and behavior. Whenever I learn a new language, it helps me rethink other languages. Recently, that language has been Perl.

Perl subroutines

Functions in Perl do not have parameter lists like most C-style languages. Instead you have to shift off the arguments within the body of the subroutine for a class, for example:

sub hash2item {
  my $self=shift;
  my $hash=shift;
  ...
}

The first argument shifted off is a reference to the object itself (named $self here). The first parameter passed to the function is $hash.

In JavaScript, this would be akin to a method like:

function hash2item (hash) {
  var self = this
}

Using $self in JavaScript functions

The $self concept made me think about vanilla functions in JavaScript. Although they don’t have a helpful this reference (i.e. global object), you can use something like $self in Perl to reference the function itself and use it as an object:

function renderElement() {
  var self = renderElement
  var element = null

  if(!self.renderedEl){
    element = document.createElement("div")
    element.className = "my-element"
    document.body.appendChild(element)
    self.renderedEl = element
  }

  self.renderedEl.style.display = "block"
}

The first time we call renderElement, we create and cache an element on the function object itself. On subsequent calls, we utilize the data stored on the object.

This example helps clean up parent scope var clutter found below when storing data:

var renderedEl
function renderElement() {
  var element

  if(!renderedEl){
    element = document.createElement("div")
    element.className = "my-element"
    document.body.appendChild(element)
    renderedEl = element
  }

  renderedEl.style.display = "block"
}

What do you think? Submit a change/correction.

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Marc is the co-author of Node.js in Action and Node.js in Practice. He writes here and for @strongloop. Works as a full-stack engineer for @applieddataconsultants.