javascript - Interpret a cumbersome conditional expression -

-

last night looking angularjs snippet manage vertical tabs menu , found expression:

if(+!!variablename)   dosomething();

sorry, can't understand mean +!!variablename how can resolve conditional expression?

this 1 way of saying if number if not null or undefined

if(+!!variablename)   dosomething();

if variablename 0, empty (""), null or undefined, translate false or else true.

for example, if

var variablename = null;

now, translate (+!!null) -> (+!true) -> (+false) -> false

similarly, if 

var variablename = "anything";

this translate (+!!"anything") -> (+!false) -> (+true) -> true

+ in case has no effect on outcome, can safely removed.

in fact, whole conditional expression can replaced by

if(variablename)   dosomething();

Comments

Post a Comment

Popular posts from this blog

How to check data type in C++? -

-
i'm new c++, i've been using python. i'm trying check type of variable of value stored in objects i'm working on. remember in python there comand isinstance use condition run commands, if next value string, a, , if it's int b. is there way check what's data type on variable in c++? example: in python had array math operation, each character in field [3,"+",2] as read array separate ints strings isinstance command if isinstance(list[0],int): aux1.append(list[0]) list=list[1:] else: if isinstance(lista[0],str): aux2.append(list[0 list=list[1:] now in c++ need similar, time each character in node linked list , again, need separate them, ints in linked list, , strings in linked list what seem struggling c++ statically , (relatively) typed language. discussion each of these terms mean refer this other question , it's explained there better could. first of should sure need...
Read more

javascript - Is getTimezoneOffset() stable during daylight saving transition? -

-
i have date time below conversion logic in javascript converting utc time passed timezone's local time. wondering logic work fine during daylight transition? if not remedy that? can't use third party library. have use pure javascript or angular js. function mytime() { var d1= document.getelementbyid("txtdate").value; var zoffset = document.getelementbyid("txtoffset").value; console.log("date1",d1); var d2 = new date(d1.replace(/ /g,'t')); var d3= d2.gettime()+(d2.gettimezoneoffset()*60000); console.log("date2",d2); console.log("date3",d3); var d4 = new date(d3 + (3600000 * zoffset)); console.log("date3",d3); console.log("date 4",d4); var d5 = d4.tolocaletimestring(); console.log("date 5",d5); ...
Read more

sql server - SQL Query returns one result, does not return 0 or NULL result -

-
i trying query list advisers , provide count of active students each. can list advisers have 1 student, exclude more 1, can not return advisers 0 or null count. select advisors.advisorid, advisors.firstname, advisors.lastname, count(case students.isactive when '1' 1 else null end) "number of students" advisors, students advisors.advisorid=students.advisorid group advisors.advisorid, advisors.firstname, advisors.lastname having count(case students.isactive when '1' 1 else null end)='1' counts active studnets, , returns advisor list advisor 1 student, advisers 0 students come blank. missing? select advisors.advisorid, advisors.firstname, advisors.lastname, count(case students.isactive when '1' 1 else null end) "number of students" advisors, students advisors.advisorid=students.advisorid group advisors.advisorid, advisors.firstname, advisors.lastname having count(case students.isactive when '1' 1 else null end) null ...
Read more