How to Check for Property Existence Using a Variable Property Name in JavaScript Objects?

How to Effectively Examine Object Property Existence Using a Property Name Variable

When working with JavaScript objects, determining whether a specific property exists is essential. However, what if you need to utilize a variable to hold the target property name?

In the provided example:

<code class="js">var myObj;
myObj.prop = "exists";
var myProp = "p"+"r"+"o"+"p";

if(myObj.myProp){
    alert("yes, i have that property");
};</code>

The code attempts to check for the existence of a property named 'myprop', which does not exist. This is because JavaScript evaluates the expression as 'myObj.myprop' instead of 'myObj.prop'.

To successfully implement this logic, you can utilize several approaches:

Using hasOwnProperty

<code class="js">var myProp = 'prop';
if(myObj.hasOwnProperty(myProp)){
    alert("yes, i have that property");
}</code>

hasOwnProperty verifies whether the object possesses a specific property, excluding inherited properties.

Using in Operator (ES5)

<code class="js">var myProp = 'prop';
if(myProp in myObj){
    alert("yes, i have that property");
}</code>

in operator examines an object's enumerable properties, including both own and inherited ones.

Using Square Brackets (ES6)

<code class="js">if('prop' in myObj){
    alert("yes, i have that property");
}</code>

In ES6, square brackets can be used interchangeably with the in operator for property existence checking.

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