debugging - Check if object exists in JavaScript -

-

how verify existence of object in javascript?

the following works:

if (!null)    alert("got here");

but fails:

if (!maybeobject)    alert("got here");

error: maybeobject not defined.

you can safely use typeof operator on undefined variables.

if has been assigned value, including null, typeof return other undefined. typeof returns string.

therefore

if (typeof maybeobject != "undefined") {    alert("got there"); }

Comments

Post a Comment

Popular posts from this blog

SAP Web Service from .NET via WCF -

-
i'm trying consume sap web service .net via wcf. i've generated proxy , have configured app.config file. here test code: webservicesap.ztest_rfcclient mywcfservice = new webservicesap.ztest_rfcclient("myendpoint"); mywcfservice.clientcredentials.username.username = "<username>"; mywcfservice.clientcredentials.username.password = "<password>"; webservicesap.ztestrfc parameter = new webservicesap.ztestrfc(); parameter.testinput = "this simple test"; webservicesap.ztestrfcresponse response = mywcfservice.ztestrfc(parameter); console.writeline(reponse.testoutput); console.readline(); the ztestrfc sap method simple function accepts input string, , outputs: "result: <the input string>" when call ztestrfc method, got null value in variable response. soap messages seem fine. soap request <messagelogtracerecord> <httprequest xmlns="http://schemas.microsoft.com/2004/06/servic...
Read more

Optimized Line drawing in QT -

-
i new qt. working on graphics. i using qwidget drawing graphics(for drawing graphics in qwidget paint event). need draw background , foreground graphics. background fixed graphics. foregrounds drawing lines. each 100 millisecond need draw 20points. drawing time 8 sec. total need draw 1600 points (total points represents contentious line). i using qtimer invoke drawing in each 100ms. first few drawing drawn fast. in middle of drawing it's become slow. the problem need draw foreground , background in each 100ms. please me fix problem. if 1 have sample code please provide. in advance. is there way draw partial area ie. particular modified region of graphics? qpainter-drawing can slow without hardware support. using qgraphicsview won't if lines visible, since internally uses qpainter anyway. if have draw 20 new points (or lines) per update , per update background gets cleared have render again, there few things try: 1) disable background autofill. see...
Read more

datetime - str to time in python -

-
time1 = "2010-04-20 10:07:30" time2 = "2010-04-21 10:07:30" how convert above string time stamp? i need subtract above timestamps time2-time1 . for python 2.5+ from datetime import datetime format = '%y-%m-%d %h:%m:%s' print datetime.strptime(time2, format) - datetime.strptime(time1, format) # 1 day, 0:00:00 edit: python 2.4 import time format = '%y-%m-%d %h:%m:%s' print time.mktime(time.strptime(time2, format)) - time.mktime(time.strptime(time1, format)) # 86400.0
Read more