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Off the top of my head: - There's both undefined and null - There's three ways to declare variable - typeof vs instanceof - for in vs for of - the way `thi

Off the top of my head: - There's both undefined and null - There's three ways to declare variable - typeof vs instanceof - for in vs for of - the way `this` works - semantics of functions called with the wrong number of args There's far more that I can't immediately recall.

throwawaymaths 2y ago
prototypes vs class
Lerc 2y ago
A lot of that is what I had in mind. Things like for...of and let fix glaring problems by introducing new things instead of changing to maintain backwards compatibility. A lot of the fixes are just removing the old broken way of doing things. I'd still probably change 'for x of ...' to implicitly be 'const x' and require let if you are doing shenanigans with changing the values. I am surprisingly ok with null and undefined. Null means not a thing, undefined means there is not even the notion of the thing. I'm pretty sure there are more than three ways to declare a variable. x=5 let x=5 var x=5 window.x=5 window["x"]=5 //arguably the same as above. Object.defineProperty(window,"x",{value:5}) Object.assign(window,{x:5}) at least
- paulddraper 2y ago
  Many of those are setting properties, not variables. A variable reference can lookup properties on the global object, or other objects with ‘with’
- int_19h 2y ago
  > Null means not a thing, undefined means there is not even the notion of the thing. If only "undefined" was consistently the same as lack of variable / collection entry, it would be understandable. But as things are, {x: 1, y: undefined} is not the same as {x: 1} in many ways - indeed, so much so that TS distinguishes between these two cases in its type system.
chuckadams 2y ago
And just for fun, `typeof null` returns `object`, which is an acknowledged bug they'll never fix because compatibility.
paulddraper 2y ago
> three ways to declare a variable FWIW Python has three (default, nonlocal, and global). And many languages have two.
codethief 2y ago
> There's both undefined and null To make matters even worse, there's a difference between setting an object property to undefined as opposed to omitting it. So one could say there are two different "undefined"s.

throwawaymaths 2y ago

prototypes vs class

Lerc 2y ago

A lot of that is what I had in mind. Things like for...of and let fix glaring problems by introducing new things instead of changing to maintain backwards compatibility. A lot of the fixes are just removing the old broken way of doing things. I'd still probably change 'for x of ...' to implicitly be 'const x' and require let if you are doing shenanigans with changing the values. I am surprisingly ok with null and undefined. Null means not a thing, undefined means there is not even the notion of the thing. I'm pretty sure there are more than three ways to declare a variable. x=5 let x=5 var x=5 window.x=5 window["x"]=5 //arguably the same as above. Object.defineProperty(window,"x",{value:5}) Object.assign(window,{x:5}) at least

paulddraper 2y ago
Many of those are setting properties, not variables. A variable reference can lookup properties on the global object, or other objects with ‘with’
int_19h 2y ago
> Null means not a thing, undefined means there is not even the notion of the thing. If only "undefined" was consistently the same as lack of variable / collection entry, it would be understandable. But as things are, {x: 1, y: undefined} is not the same as {x: 1} in many ways - indeed, so much so that TS distinguishes between these two cases in its type system.

chuckadams 2y ago

And just for fun, `typeof null` returns `object`, which is an acknowledged bug they'll never fix because compatibility.

paulddraper 2y ago

> three ways to declare a variable FWIW Python has three (default, nonlocal, and global). And many languages have two.

codethief 2y ago

> There's both undefined and null To make matters even worse, there's a difference between setting an object property to undefined as opposed to omitting it. So one could say there are two different "undefined"s.