JavaScript history: undefined

By -
Two tweets by Brendan Eich shed light on the history of JavaScript having both undefined and null [1].




The first version of JavaScript did not have exception handling, which is why JavaScript so often converts automatically [2] and/or fails silently (tweet).


JavaScript copied Java’s approach of partitioning values into primitives and objects [3]. null is the value for “not an object”. The precedent from C (but not from Java) is to convert null to 0 (C has pointers, not references and lets you perform arithmetic with pointers).


Remaining problem: In JavaScript, each variable can hold both primitives and objects. In Java, a variable’s static type limits it to either kind of value. We therefore need a value for “neither a primitive nor an object”. That value could be null, but at the time, Eich wanted something that wasn’t “reference-y” (associated with objects) and did not convert to 0 (tweet). Now you know why undefined and null are converted to different numbers:


    > Number(undefined)
    NaN
    > Number(null)
    0


References:


  1. JavaScript quirk 2: two “non-values” – undefined and null

  2. JavaScript quirk 1: implicit conversion of values

  3. Categorizing values in JavaScript


Comments

Post a Comment

Popular posts from this blog

Steve Lopez and the Importance of Newspapers

By -
Image
It has been one year since I cancelled my subscriptions to The New York Times and the Los Angeles Times . In that time, I continued to read both publications online. My assessment of this experiment is that reading newspapers and journalism online is vastly inferior to the hard copy thrown on my porch each morning. So I restarted my subscription to the Los Angeles Times and I have made it a point to buy The New York Times as often as I pass one of those coin boxes or my local news stand. The catalyst for this re-evaluation resulted from catching the film, The Soloist on cable last week. I liked the movie, although the scenes I found most interesting were the ones that showed columnist Steve Lopez at work. I realized the book was sitting in my “to-read” stack, so I pulled it and began reading. The book, as I expected, is better than the film. Lopez clearly addresses the revolution occurring in journalism, and worries about his future with the paper even as he researches and writes...
Keep reading

Ideas for fixing unconnected computing

By -
I traveled quite a bit recently and got exposed to a negative aspect of current technology: Things work well if you have a solid internet connection with no traffic limits and are plugged into a power outlet. Otherwise, things do not work well at all. This blog post describes the problems that arise and suggests solutions. Managing data traffic Cell phones are quite good at conserving traffic, laptops much less so. This becomes a problem when your laptop has a mobile connection (e.g., via tethering or in a hotel with data caps). I once accidentally started iTunes in such a situation and immediately used up my daily allowance of traffic. Similarly, mobile email is frugal with traffic (only the current folder is updated, attachments are only downloaded on demand, etc.), desktop email is usually not. How can this be handled better? I’d like to see three traffic modes for all operating systems: “full”, “restricted”, “minimal”: In full traffic mode , all data transfers are allowed and happe...
Keep reading

Omar to kill me

By -
Image
  The sentence “ Omar m’a tuer ” is unintelligible French, as if it had been written by an illiterate person. At first sight, Mme Ghislaine Marchal —the author of those words in blood—seems to be saying that she had been killed by Omar in her villa at Mougins (Alpes-Maritimes). But why would that dying French lady have used such poor grammar? On that flimsy evidence, in 1991, the Moroccan gardener Omar Raddad was condemned and jailed. But he persisted non-stop upon his innocence. In 1998, he was liberated, and now lives in Morocco. A recent analysis of DNA specimens from the scene of the crime provides new facts. Four males, none of whom was Omar Raddad, have left traces of their presence. Will the real murderer be identified at last?
Keep reading