Is if document getElementById something null identical to if document getElementById something

Question

When I want to check if an element exists in a page  Are these two checks the same   Is there a better more compact way to check the existence   What if I want to check if the value        Can this be included in this check as well

User · Answer

document getElementById  something   can be  undefined   Usually  thought not always  it s sufficient to do tests like if  document getElementById  something

User · Answer

Cleanest version specially good if you just want to get the  value from the element   document getElementById  elementsid     function if exists    function if doesnt exists

User · Answer

jquery will provide you with this and more      if     something   val       do stuff    It took me a couple of days to pick it up  but it provides you with you with so much more functionality  An example below   jQuery document  ready function            finds closest element with class divright left and      makes all checkboxs inside that div class the same as selectAll                       selectAll   click function               this  closest   divright   find   checkbox   attr  checked   this checked

User · Answer

It s better  but wordier  to use   var element   document getElementById  something    if  element    null  amp  amp  element value              Please note  the first version of my answer was wrong   var element   document getElementById  something    if  typeof element      undefined   amp  amp  element value              because getElementById   always return an object  null object if not found  and checking for undefined  would never return a false  as typeof null      undefined  is still true

User · Answer

Just do it like this   if  document getElementById  someId      Some code  Note the NOT     in the expresion      If element with id  someId  does not exist expresion will return TRUE  NOT FALSE     TRUE  or  false     true   try this code    lt  DOCTYPE html gt   lt html gt       lt head gt           lt meta charset  UTF-8  gt           lt meta name  format-detection  content  telephone-no  gt           lt meta name  viewport  content  user-scalable no  initial-scale 1  minimum-scale 1  maximum-scale 1  width device-width  height device-height  target-densitydpi device-dpi  gt           lt title gt Test lt  title gt       lt  head gt       lt body gt         lt script gt  var createPerson   function  name        var person      if   document getElementById name             alert  Element does not exist  Let s create it           person   document createElement  div      add argument name as the ID of the element       person id   name    append element to the body of the document       document body appendChild person         else           alert  Element exists  Lets get it by ID           person   document getElementById name             person innerHTML    HI THERE          run the function  createPerson  someid               lt  script gt          lt  body gt   lt  html gt    Try this in your browser and it should alert  Element does not exist  Let s create it     Now add    lt div id  someid  gt  lt  div gt    to the body of the page and try again  Voila

User · Answer

Yeah   Try this   lazy evaluation should prohibit the second part of the condition from evaluating when the first part is false null   var someval   document getElementById  something   if  someval  amp  amp  someval value  lt  gt

User · Answer

A reference to an element will never look  falsy   so leaving off the explicit null check is safe   Javascript will treat references to some values in a boolean context as false  undefined  null  numeric zero and NaN  and empty strings  But what getElementById returns will either be an element reference  or null  Thus if the element is in the DOM  the return value will be an object reference  and all object references are true in an if    test  If the element is not in the DOM  the return value would be null  and null is always false in an if    test   It s harmless to include the comparison  but personally I prefer to keep out bits of code that don t do anything because I figure every time my finger hits the keyboard I might be introducing a bug     Note that those using jQuery should not do this   if      something                    because the jQuery function will always return something  truthy   mdash  even if no element is found  jQuery returns an object reference  Instead   if      something   length                  edit  mdash  as to checking the value of an element  no  you can t do that at the same time as you re checking for the existence of the element itself directly with DOM methods  Again  most frameworks make that relatively simple and clean  as others have noted in their answers

[javascript] Is if(document.getElementById('something')!=null) identical to if(document.getElementById('something'))?

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