javascript - undefined and NaN, convert to boolean value implicitly vs explicitly -


i'm learning javascript following book "you dont know js".

in section "type & grammer", when discussing implicit vs explicit boolean convertion, author mentioned 

//come function make sure 1 argument truthy  //implicit convertion function onlyone() {   var sum = 0;   (var i=0; < arguments.length; i++) {       // skip falsy values. same treating       // them 0's, avoids nan's.       if (arguments[i]) {           sum += arguments[i];       }   }   return sum == 1; }  //explicit convertion function onlyone() {   var sum = 0;   (var i=0; < arguments.length; i++) {       sum += number( !!arguments[i] );   }   return sum === 1; }

is explicit coercion form of utility "better"? avoid nan trap explained in code comments. but, ultimately, depends on needs. think former version, relying on implicit coercion more elegant (if won't passing undefined or nan), , explicit version needlessly more verbose.

my question is, nan trap author talking about? thought when undefined , nan converted boolean value, regardless of whether converted implicitly or explicitly, both results in false. , passing undefined , nan implicit function ok, right?

i think example of real explicit check be...

function onlyone() {   var sum = 0;   (var i=0; < arguments.length; i++) {       sum += boolean( arguments[i] );   }   return sum == 1; }

this of course avoid / guard against nan , should return false if no arguments present; if no arguments truthy , of course -if more 1 arguments truthy.


Comments

Post a Comment

Popular posts from this blog

php - Vagrant up error - Uncaught Reflection Exception: Class DOMDocument does not exist -

i've set bento/ubuntu-16.04 vagrant box using php 5.6, , getting following error quite few times when try , run shell script: "uncaught reflection exception: class domdocument not exist". i've tried adding following top of script (not together), each no success: "sudo apt-get install php5.6-xml", "sudo apt-get install php5-xml", "sudo apt-get install php-dom" i've tried resetting server "sudo service apache2 restart". does have suggestions?
Read more

vue.js - Create hooks for automated testing -

Image
qa guys complained can't automate frontend testing. because our html looks same outside. lazy hack did this <template> <div :role="$options.name"> ... </div> </template> <script> export default { name: 'vmcomponentname' } </script> which takes name script , applies html. in browser get: <div role="vmcomponentname"> ... </div> line :role="$options.name" goes in every component. is there dry er solutions? please share. additional details i'll explain in details looking for. imagine have vmusercreate form creates user. test case can create user . to automatically test without role, have use following selector: .wrapper > .wrapper > .wrapper > .submit-button the test extremely brittle (will break lot). if use roles can use [role="vmusercreateform"] .submit-button selector. many folds less brittle. so basically, i'm ...
Read more

Add new key value to json node in java -

i have json file : { "id":1, "name":"abc", "addressdetails": { "city":"newyork" } } i wanted add 1 more key-value ("pincode" : "414141") node 'addressdetails'. i tried using : objectmapper mapper = new objectmapper(); jsonnode root = mapper.readtree(new file("d://test.json")); objectnode node = mapper.createobjectnode(); node.with("addressdetails").put("pincode", "414141"); but it's not getting added, there way can ? you can try you should modify file path objectmapper mapper = new objectmapper(); objectnode nodes = mapper.readvalue(new file("d:\\test.txt"), objectnode.class); nodes.with("addressdetails").put("pincode", "414141"); mapper.writer().writevalue(new file("d:\\test.txt"), nodes);
Read more