for (i = 0; i < 10; i++) {
doStuff();
}
That's the JavaScript code that I Want to convert to CoffeeScript.
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Try js2.coffee tooPeterM– PeterM2017-10-17 19:58:33 +00:00Commented Oct 17, 2017 at 19:58
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3 Answers
doStuff() for i in [0 .. 9]
This is explained on the introduction page: http://coffeescript.org/#loops
Edit/Update by JP:
The exact translation is:
doStuff() for i in [0...10]
You need to be careful with the ".." vs "...", for example:
count = 0
doStuff() for i in [0..count] #still executes once!
So you think, no problem... I'll just loop until count-1!
count = 0
doStuff() for i in [0..count-1] #executes twice!! '0' and then '-1'
Literal translation of:
for (var i = 0; i < someCount; ++i)
doStuff()
is
for i in [0...someCount]
doStuff()
4 Comments
Trevor Burnham
Right, or to translate it literally,
for i in [0...10]. Two dots (..) means "up to and including," while three dots (...) means "up to but not including." It's a Ruby-ism.
jontro
@JP Well if you introduce a variable in the loop the code will behave differently. For example it will determine runtime which way the counter should go. 0 .. 0 should execute once. 0 .. -1 should execute twice.
JP Richardson
@Bengt exactly. I thought it was an important to modify the answer so that would be internet searchers don't get confused. AFAIR, the CoffeeScript docs aren't clear on this. I got burned by it, I don't want others. I think my additional examples spell this out for people.
The marked answer is functionaly correct but the generated code doesn't match the original javascript.
The right way (read, the one closest to the following javascript)
for (i = 0; i < 10; i++) {
doStuff();
}
is doStuff() for i in [0..someCount] by 1
Note the by 1 on the for loop.
Now this code, still creates an extra _i variable. If you can't live with it, then use the following:
i=0
while i<=someCount
doStuff()
i++
Comments
Previous answers work. However, dropping the i generates it better for me:
for [0...10]
doStuff()
or
doStuff() for [0...10]
The other solutions add an extra iterator variable i for you to use inside of the loop, for example doStuff(i), but from http://coffeescript.org/v1/#loops:
If you don’t need the current iteration value you may omit it:
browser.closeCurrentTab() for [0...count]
In detail, the translation of for i in [0...10] is for (i = j = 0; j < 10; i = ++j), whereas the translation of for [0...10] is for (i = 0; i < 10; i++).
Note the discussion in other comments about 2-dots versus 3-dots ([0..9] vs. [0...10]).
