typeof - some unexpected results

[Inger Hohler]

I am trying to explore 'return', closure etc. and wanted to try to find examples of returning different data types.
I tried to follow the list here https://www.w3schools.com/js/js_datatypes.asp and found some unexpected results, the code which causing issues is on a yellow background.

Are there anyone here who can help explain what is happening? Or if it's a good idea that BabyHints reacts to what I place in println brackets? I think one of the things I saw is related to https://github.com/Khan/live-editor/issues/553 but I don't know if it's a different thing than those already reported, and should be added to the list.

primitive data types
*string 

println(typeof("hope & pray")); returns string

I can use return for instance to make and return a copy of a string which has been corrected so that "&" reads as "and".

*number
println(typeof(5)); and println(typeof(pileUpCounters())); which is a user defined function that returns a number, both returned 'number'

KA covers examples of how to use it.
... but println(typeof(draw())); returns 'number' which I did not expect at all. It's a function call, and I had no idea that it could return a number. The documentation does not say so.

*boolean
println(false); returns 'boolean' which is expected
println(typeof(1<3)); returns 'boolean' which makes sense to me as we've seen how 'return' works for booleans in Project Memory on KA.
KA covers of how to how to use it.

*undefined
println(typeof(sugar)); returns 'undefined' ,which is correct as I had not defined it

println(typeof(background(255)));  this is a function call for a function which does not return a value, I think. So it makes sense that it's undefined.

println(typeof(sugar())); makes OhNoes pop up saying 'sugar is not defined' which is correct, the function has not been defined. But it's problematic if I try to check the type. I had expected undefined since this is a function call which does not return anything

complex data types
*function
println(typeof(random)); returns a function, which is as expected

println(typeof(pileUpMoney)); returns a function because I have defined pileUpMoney as a function.

*object
println(typeof(canvas)); returns 'undefined' which surprised me at first because there is such as thing as the canvas object, but then I realized that it's probably because the canvas object is not a javascript object

var d = new Date(); println(typeof(d)); returns 'string' which I did not expect for something called a date object.which is a part of Javascript.
println(typeof(thingy)); returns 'object' when I've defined thingy as an object, which is expected

and a known problem child,

*null - can't create an example as the type of null is 'object' which I'll just have to accept as an anomaly or bug.

[Larry Serflaten]

 Inger Hohler wrote:

I am trying to explore 'return', closure etc. and wanted to try to find examples of returning different data types.

 

... but println(typeof(draw())); returns 'number' which I did not expect at all. It's a function call, and I had no idea that it could return a number. The documentation does not say so.

That may be KA's doing.  if you use;   println(draw);

You will see that it prints a function that returns 0.  I do not see that in the PJS code that I have (Vers. 1.4.8) In that code draw is simply an undefined variable.  Its the user who actually assigns the function.

 

println(typeof(sugar())); makes OhNoes pop up saying 'sugar is not defined' which is correct, the function has not been defined. But it's problematic if I try to check the type. I had expected undefined since this is a function call which does not return anything

It can not be resolved because 'typeof' can not access the object.

You could just define a function that does not return anything and test that:

var nope = function(){};

println(typeof nope());

And you can try to intercept the error before Oh Noes gets it:

try{

    println(typeof sugar());

}catch(e){

    println(e);

}

But it will tell you pretty much the same thing:  ReferenceError: sugar is not defined 

var d = new Date(); println(typeof(d)); returns 'string' which I did not expect for something called a date object.which is a part of Javascript.

Yes "d"  should be an object type, but KA still has issues with the Date object:

https://github.com/Khan/live-editor/issues/612

FYI:   typeof  is an operator,  not a function.  Check your W3schools examples, they do not use parentheses.

LFS

[Bob Lyon]

The typeof null is "object" which is neither an anomaly or bug.  null is the only object that when coerced to a boolean is false.  It shares that rare coercion status with zero (the only number), "" (the only string), and undefined.

[Larry Serflaten]

Bob Lyon wrote:

The typeof null is "object" which is neither an anomaly or bug.  null is the only object that when coerced to a boolean is false.  It shares that rare coercion status with zero (the only number), "" (the only string), and undefined.

That certainly makes more sense than the ECMA Specification:

"The value of the null literal null is the sole value of the Null type, namely null."

:-)

LFS