this post was submitted on 05 Oct 2023
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Oh man, you've got me itching to get into the intricacies of JavaScript...
One fun example of the difference: when doing arithmetic operations,
nullis indeed converted to 0, butundefinedis converted to NaN. This has to do withnullbeing an assigned value that represents empty, whereasundefinedis not actually a value but a response indicating that there was no value assigned in the first place.You can explicitly assign undefined to a variable though.
Another fun fact about JavaScript is that
undefinednever used to be a keyword. If you didvar foo = undefined,foowould indeed have a value ofundefined, but it was only because there was no variable calledundefinedin scope!You could do
var undefined = 42thenvar foo = undefinedwould actually setfooto42!window.undefined = 42would break all sorts of things.Thankfully this was fixed with ES5 in 2009, although it took a few years for browsers to make the change.
javascript moment