actually i think it has to do with the index variable "var i" of the for loop and that by putting the body of the loop into a function "get_http", where the value of "i" in each execution of the loop body is "kept alive" by creating a seperate scope for each execution of the body, the the anonymous callback "function (r)..." body will use the value of "i" that existed during each execution of the for loops body. If u do not create that scope, every anonymous callback will use the value of "i" that existed after the loop finishes, which is the "max i" value (i<3)...
2015-01-18 15:44 GMT+01:00 <[email protected]>: > Hi there... I'm just going through the learnyounode exercises (so > obviously a complete node.js beginner!) - and was proceeding quite > confidently until I hit upon the 'juggling async' exercise. I have to admit > tearing my hair out here and eventually cheating to get the 'official > answer'. More frustrating was how close I was... and I am still not sure > why mine does not work. I apologise if I am being stupid (very likely) - > but I think it would really help my understanding to get to the bottom of > this. > Anyway, what I did was this: > > var http = require('http'); > var bl = require('bl'); > > var htmls = []; > > var count = 0; > > for( var i = 0; i<3; i++){ > > http.get( process.argv[2+i], function( r ){ > r.pipe(bl(function( err, buf ){ > count++; > htmls[ i ] = buf.toString(); > if ( count == 3 ){ > print_results(); > } > })) > }); > } > > > function print_results(){ > for( var j=0; j<3; j++ ){ > console.log( htmls[j] ); > } > } > > > I then run e.g. > node ex9.js http://www.google.com http://www.yahoo.com > http://www.reuters.com > > and get: > undefined > undefined > undefined > > > > To get the correct answer, all I need to do is stick the stuff in the > first 'for' loop in a function and instead loop through calling the > function: > > for( var i = 0; i<3; i++){ get_http(i) } > > function get_http(i){ > http.get( process.argv[2+i], function( r ){ > r.pipe(bl(function( err, buf ){ > count++; > htmls[ i ] = buf.toString(); > if ( count == 3 ){ > print_results(); > } > })) > }); > } > > Now it works! But why? I can see that 'i' is scoped differently in the > second (correct) arrangement, but still don't see how it is it produces > different results. > Very much appreciate any light that could be shed on this (for a complete > beginner!) > Thanks :) > > > > -- > Job board: http://jobs.nodejs.org/ > New group rules: > https://gist.github.com/othiym23/9886289#file-moderation-policy-md > Old group rules: > https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines > --- > You received this message because you are subscribed to the Google Groups > "nodejs" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/nodejs/c9baf277-19bc-4d83-8b21-045dc1102079%40googlegroups.com > <https://groups.google.com/d/msgid/nodejs/c9baf277-19bc-4d83-8b21-045dc1102079%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- Job board: http://jobs.nodejs.org/ New group rules: https://gist.github.com/othiym23/9886289#file-moderation-policy-md Old group rules: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines --- You received this message because you are subscribed to the Google Groups "nodejs" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/nodejs/CAN5%2BLUsMXXUYP6mG%3DGNS0-tfDzke8YNXb8tYu6KgS52NoEyEoA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
