How does jquery determine whether an object exists?

Jquery method to determine whether an object exists: use the length attribute to determine whether the number of elements in the object is greater than 0. If it is greater than 0, the object exists, otherwise it does not exist; syntax "if ($(selector).length > ; 0) {//Exists}else {//Does not exist}".

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1. Traditional Javascript writing method

obj = document.getElementById("someID"); 
if (obj){ 
   obj.innerText("hi"); 
}

In jQuery, var obj = $("#id") returns object regardless of whether the id control exists, so if(obj) cannot be used to determine whether the control exists

2. jQuery determines whether the object exists

Method 1:

if ($('#target_obj_id').length > 0) {
//如果大于0 标识 id 为target_obj_id的对象存在，否则不存在 
   //对象存在的处理逻辑 
} else { 
   //对象不存在的处理逻辑 
}

Method 2:

if ($('#target_obj_id')[0]) { 
  //对象存在的处理逻辑 
} else { 
  //对象不存在的处理逻辑 
}

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