Summary of methods to determine whether an object exists in jQuery_jquery

If the following jQuery code is used to determine whether an object exists, it cannot be used.

if($("#id")){
  //...
}else{
  //...
}

Because $("#id") will return object regardless of whether the object exists.

To use correctly to determine whether an object exists, use:

if($("#id").length>0){
  //...
}else{
  //...
}

Use the length property of the jQuery object to determine if > 0 exists.

or

if($("#id")[0]){
  //...
}else{
  //...
}

Or directly use native Javascript code to judge:

if(document.getElementById("id")){
  //...
}else{
  //...
}