node.js - Why does my export stop updating when the array it references is sliced? -


i've been using node.js few years , believed understood how exports worked, edge case today has left me bit confused. code when simplified, behaved following:

a.js

var history = [] var  = 0  exports.updatehistory = function(){     history.push(i)     i++      if(history.length > 10){         history = history.slice(5)     } }  exports.history = history

b.js

var = require('./a')  setinterval(function(){     a.updatehistory()     console.log(a.history) }, 200)

i expected output of following:

[ 0 ] [ 0, 1 ] [ 0, 1, 2 ] [ 0, 1, 2, 3 ] [ 0, 1, 2, 3, 4 ] [ 0, 1, 2, 3, 4, 5 ] [ 0, 1, 2, 3, 4, 5, 6 ] [ 0, 1, 2, 3, 4, 5, 6, 7 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] [ 5, 6, 7, 8, 9, 10 ] [ 5, 6, 7, 8, 9, 10, 11 ] [ 5, 6, 7, 8, 9, 10, 11, 12 ] [ 5, 6, 7, 8, 9, 10, 11, 12, 13 ] [ 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 ] [ 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ] [ 10, 11, 12, 13, 14, 15 ] [ 10, 11, 12, 13, 14, 15, 16 ] [ 10, 11, 12, 13, 14, 15, 16, 17 ] ...

but instead, output:

[ 0 ] [ 0, 1 ] [ 0, 1, 2 ] [ 0, 1, 2, 3 ] [ 0, 1, 2, 3, 4 ] [ 0, 1, 2, 3, 4, 5 ] [ 0, 1, 2, 3, 4, 5, 6 ] [ 0, 1, 2, 3, 4, 5, 6, 7 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]

i able solve problem adding exports.history = history after slices each time, implying slice call somehow changing export's reference, have no idea why be. can explain behavior me?

thanks

you're updating local variable , not exported value.

change this:

exports.history = history = history.slice(5)

the reason needed because array.slice() returns copy of portion of array , not visible outside of module (exports.history still references original array).


Comments

Post a Comment

Popular posts from this blog

Is there a better way to structure post methods in Class Based Views -

i'm using class based views in django , never specify url in ajax calls , omit action parameter in form because know these requests go through post method of class based view. notice view - profile page make many requests depending on user updating on page - post method become convoluted , if/else mess example: def post(self, request, *args, **kwargs): # handle user changing available date if request.post.get('availabledate') != none: self.updateavailabledate(request) return jsonresponse({'result':'success'}) if request.post.get('newprojectname') != none: creative_user = creativeuserprofile.objects.get(id = request.user.id) project = project.create_project(creative_user, request.post['newprojectname']) project.save() return jsonresponse({'projectid': project.id }) if request.post.get('projectimage') != none , request.files['file']: proj
Read more

performance - Why is XCHG reg, reg a 3 micro-op instruction on modern Intel architectures? -

i'm doing micro-optimization on performance critical part of code , came across sequence of instructions (in at&t syntax): add %rax, %rbx mov %rdx, %rax mov %rbx, %rdx i thought had use case xchg allow me shave instruction , write: add %rbx, %rax xchg %rax, %rdx however, dimay found agner fog's instruction tables , xchg 3 micro-op instruction 2 cycle latency on sandy bridge, ivy bridge, broadwell, haswell , skylake. 3 whole micro-ops , 2 cycles of latency! 3 micro-ops throws off 4-1-1-1 cadence , 2 cycle latency makes worse original in best case since last 2 instructions in original might execute in parallel. now... cpu might breaking instruction micro-ops equivalent to: mov %rax, %tmp mov %rdx, %rax mov %tmp, %rdx where tmp anonymous internal register , suppose last 2 micro-ops run in parallel latency 2 cycles. given register renaming occurs on these micro-architectures, though, doesn't make sense me done way. why wouldn't register renamer
Read more

jquery - Responsive Navbar with Sub Navbar -

good day, forgive me nav vocabulary not best. if question confusing apologize. i'm working on navigation bar needs centered on page @ 768px , above. items in nav open (or perhaps toggle) subnav lives directly below. these nav should appear centered on page. i have been able work through responsive portion of nav bar, having main items align vertically , sub nav menu of each item roll out below, , gave them indent separation. working well. however, issue not responsive side, behavior @ width greater 768px. happens toggling menu's sub navigation pushes other main items down page below sub nav. here's code: $(document).ready(function () { //stick in fixed 100% height behind navbar don't wrap $('#slide-nav.navbar-inverse').after($('<div class="inverse" id="navbar-height-col"></div>')); $('#slide-nav.navbar-default').after($('<div id="navbar-height-col"></d
Read more