How to determine whether an object exists in jquery

Jquery method to determine whether an object exists: 1. Use traditional Javascript writing method, the code is [obj = document.getElementById("someID")]; 2. Use jQuery to determine the object. If it is greater than 0, identify the id. exist.

The operating environment of this tutorial: windows10, jquery2.2.4, this article is applicable to all brands of computers.

How jquery determines whether an object exists:

1. Traditional Javascript writing method

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

In jQuery, var obj = $ ("#id")No matter whether the id control exists or not, object is returned, 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 
}

Related free learning recommendations: JavaScript (video)

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