这是检查对象是否具有属性的最佳方法

Question

I want to ask which is the right way to check if an ajax response object has a property . I googled and what I found is that there are different ways to approach this.

For example:

    if(ajaxResponse.hasOwnProperty('someProperty')){
       //do blah blah
    }

but there are other ways for sure, for example :

    if(typeof ajaxResponse.someProperty !== 'undefined')){
       //do blah blah
    }

So I am guessing there are some pros and cons can you please share these with me.

Thanks

Answer 1

Let's say your an object is something like the one showed below...

var person = {
    name: "Nicholas"
};

there are plenty of methods using which you can check for this....

Method 1

person.hasOwnProperty("name")

Method 2

if ("name" in person){
    //property exists
}

Method 3 (NOT RECOMMENDED)

//doesn't accurately test for existence
if (person.name){
    //yay! property exists!
}

If you just want to check for the existence of properties, and not necessarily what their value might be, then you have two safe options: hasOwnProperty() and the in operator. The hasOwnProperty() property method should be used if you want to detect own properties only. If you want to test property existence and don't care if it's an own property or an object property, then the in operator is the one to use.

Source

Answer 2

 $.ajax({
            type: "POST",
            url: "frmSample.aspx/LoadSample",
            data: '',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function (data) {     
               var jsonData = $.parseJSON(data.d);    
            },
            error: function OnError(xhr) {           
            }
        });

Suppose if any error occurs in ajax call the response goes directly to the error , it will not go to success . If empty data is passed as result, then data.d would be ''. So, it is neccessary to check whether data.d is empty or not before parsing. If the resultant is Json, parse the json as follows

var jsonData = $.parseJSON(data.d);

If jsonData.length == 0 , no property is there for the result. There are many ways of checking the property in json response. This is one way of doing it in simple. Directly check the jsonData. PropertyName != null or not.

Answer 3

the easiest way imo is:

if (ajaxResponse.someProperty){
//do stuff
}

Except the property is a boolean. Then this would not necessarily work as wanted :)