(This is a snapshot of my old weblog. New posts and selected republished essays can be found at raganwald.com.)
Tuesday, May 09, 2006
JavaScript Pop Quiz
In essay or point form, compare and contrast:
and
Do not limit yourself to describing the run-time behaviour as specified in the language specification. Discuss the implications of each choice in the broader context of programming and software design.
Hint 1: Consider the possibility that these statements may be executed more than once, that this_cell may refer to different objects when these statements are executed more than once, and that dt_current_day may have different values when these statements are executed more than once.
Hint 2: SICP.
Hint 3:
Hint 4: JavaScript Pop Quiz Remarks
In essay or point form, compare and contrast:
thisCell.onclick = function() { set_datetime( dt_current_day.valueOf(), true); };
and
thisCell.onclick =
function (day) {
return function() { set_datetime( day, true); };
}(dt_current_day.valueOf());Do not limit yourself to describing the run-time behaviour as specified in the language specification. Discuss the implications of each choice in the broader context of programming and software design.
Hint 1: Consider the possibility that these statements may be executed more than once, that this_cell may refer to different objects when these statements are executed more than once, and that dt_current_day may have different values when these statements are executed more than once.
Hint 2: SICP.
Hint 3:
Hint 4: JavaScript Pop Quiz Remarks
Comments on “JavaScript Pop Quiz”:
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Variation A is likely the one I would use as it appeals to me aestheticly speaking.
Variation B is more is nice because valueOf() gets called one time (at assign time).
If you have a page that gets opened at 11:59pm that uses this code, variation A would be useful if you wanted to accurately represent the day at the time of a click; variation B would represent the date of the instantiation of the object. Both have their uses.
The efficiency of B would be more applicable to a system that wasn't time-specific. In this example, the dt_current_day.valueOf() call defines the usage.
Variation B is more is nice because valueOf() gets called one time (at assign time).
If you have a page that gets opened at 11:59pm that uses this code, variation A would be useful if you wanted to accurately represent the day at the time of a click; variation B would represent the date of the instantiation of the object. Both have their uses.
The efficiency of B would be more applicable to a system that wasn't time-specific. In this example, the dt_current_day.valueOf() call defines the usage.
Compare and contrast? BS ahead:
Since this is javascript, it runs on the client computer. Further, it only runs when the the cell is clicked and it isn't a global function for everything to use. So the performance of the function as well as the end result of the function is not in question here.
My first knee-jerk reaction to the code was "the second block is definitely the way to go, because that code is more generic and reusable." The first block has hardcoded data (the current date time) embedded in it's function defintion. So it is inherently inflexible. I cannot change the date to tomorrow, or yesterday.
Did I pass?
Since this is javascript, it runs on the client computer. Further, it only runs when the the cell is clicked and it isn't a global function for everything to use. So the performance of the function as well as the end result of the function is not in question here.
My first knee-jerk reaction to the code was "the second block is definitely the way to go, because that code is more generic and reusable." The first block has hardcoded data (the current date time) embedded in it's function defintion. So it is inherently inflexible. I cannot change the date to tomorrow, or yesterday.
Did I pass?
A: Click on any cell to set the date to the last day of the week.
B: Click on any cell to set the date to that day of the week.
The problem with A is that all cell functions share the same closure and the same date value, since they all reference the same object (pass by stack?).
B solves that by creating another closue with a different date reference for each cell.
B: Click on any cell to set the date to that day of the week.
The problem with A is that all cell functions share the same closure and the same date value, since they all reference the same object (pass by stack?).
B solves that by creating another closue with a different date reference for each cell.
Ok! I got it now. You should have purchased a javascript calendar. :)
I can't understand the difference between the two code snippets. However, wouldn't you write that code differently so that people like me who come in later for maintenance don't screw it up?
I can't understand the difference between the two code snippets. However, wouldn't you write that code differently so that people like me who come in later for maintenance don't screw it up?
"wouldn't I write the code differently for maintenence..."
Hmmm. First, why would I hire someone as a programmer if they couldn't maintain either style of code? Doesn't that mean they don't know their job?
Second, let's say there are two kinds of programmers, call them As and Cs. If you tell the As that they have to write programs for the benefit of the Cs, why not hire the Cs to begin with?
Oh wait, that's what most companies wind up doing, because the As chafe when told to pretend to be Cs.
Hmmm. First, why would I hire someone as a programmer if they couldn't maintain either style of code? Doesn't that mean they don't know their job?
Second, let's say there are two kinds of programmers, call them As and Cs. If you tell the As that they have to write programs for the benefit of the Cs, why not hire the Cs to begin with?
Oh wait, that's what most companies wind up doing, because the As chafe when told to pretend to be Cs.
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