How to check if object property exists with a variable holding the property name?

Question

I am checking for the existence of an object property with a variable holding the property name in question.

var myObj; myObj.prop = "exists"; var myProp = "p"+"r"+"o"+"p";  if(myObj.myProp){     alert("yes, i have that property"); }; 

This is undefined because it's looking for myObj.myProp but I want it to check for myObj.prop

Answer 1

var myProp = 'prop'; if(myObj.hasOwnProperty(myProp)){     alert("yes, i have that property"); } 

Or

var myProp = 'prop'; if(myProp in myObj){     alert("yes, i have that property"); } 

Or

if('prop' in myObj){     alert("yes, i have that property"); } 

Note that hasOwnProperty doesn't check for inherited properties, whereas in does. For example 'constructor' in myObj is true, but myObj.hasOwnProperty('constructor') is not.

Answer 2

You can use hasOwnProperty, but based on the reference you need quotes when using this method:

if (myObj.hasOwnProperty('myProp')) {     // do something } 

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty

Another way is to use in operator, but you need quotes here as well:

if ('myProp' in myObj) {     // do something } 

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in