How can I detect if a selector returns null

Question

What is the best way to detect if a jQuery-selector returns an empty object  If you do   alert     notAnElement       you get  object Object   so the way I do it now is   alert     notAnElement   get 0      which will write  undefined   and so you can do a check for that  But it seems very bad  What other way is there

User · Answer

This is in the JQuery documentation   http   learn jquery com using-jquery-core faq how-do-i-test-whether-an-element-exists     alert       notAnElement    length    Not null     Null

User · Answer

The selector returns an array of jQuery objects  If no matching elements are found  it returns an empty array  You can check the  length of the collection returned by the selector or check whether the first array element is  undefined    You can use any the following examples inside an IF statement and they all produce the same result  True  if the selector found a matching element  false otherwise       notAnElement   length  gt  0     notAnElement   get 0      undefined     notAnElement   0      undefined

User · Answer

I like to use presence  inspired from Ruby on Rails     fn presence   function          return this length     0  amp  amp  this      Your example becomes   alert     notAnElement   presence       No object found      I find it superior to the proposed   fn exists because you can still use boolean operators or if  but the truthy result is more useful  Another example    ul    elem find  ul   presence          lt ul class  foo  gt    appendTo  elem   ul append

User · Answer

My preference  and I have no idea why this isn t already in jQuery     fn orElse   function elseFunction      if   this length        elseFunction             Used like this       notAnElement   each function        alert  Wrong  it is an element      orElse function       alert  Yup  it s not an element         Or  as it looks in CoffeeScript       notAnElement   each - gt    alert  Wrong  it is an element   return  orElse - gt    alert  Yup  it s not an element

User · Answer

You may want to do this all the time by default  I ve been struggling to wrap the jquery function or jquery fn init method to do this without error  but you can make a simple change to the jquery source to do this  Included are some surrounding lines you can search for  I recommend searching jquery source for The jQuery object is actually just the init constructor  enhanced   var   version    3 3 1         Define a local copy of jQuery   jQuery   function  selector  context             The jQuery object is actually just the init constructor  enhanced         Need init if jQuery is called  just allow error to be thrown if not included      var result   new jQuery fn init  selector  context        if   result length     0           if  window console  amp  amp  console warn  amp  amp  context      failsafe             if  selector    null              console warn              new Error        selector      selected nothing  Do   sel   failsafe   to silence warning  Context   context                                           return result             Support  Android  lt  4 0 only      Make sure we trim BOM and NBSP   rtrim       s uFEFF xA0     s uFEFF xA0    g   jQuery fn   jQuery prototype       Last but not least  you can get the uncompressed jquery source code here  http   code jquery com

User · Answer

if       anid   length       alert  element s  found      else     alert  nothing found

User · Answer

I like to do something like this     fn exists   function        return this length  gt  0   this   false      So then you can do something like this   var firstExistingElement            iDontExist   exists              lt -returns false          iExist   exists                  lt -gets assigned to the variable          iExistAsWell   exists            lt -never runs  firstExistingElement doSomething         lt -executes on  iExist   http   jsfiddle net vhbSG

User · Answer

My favourite is to extend jQuery with this tiny convenience     fn exists   function          return this length     0      Used like       notAnElement   exists      More explicit than using length

[jquery] How can I detect if a selector returns null?

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