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

Checking Object Property Existence with a Variable

In JavaScript, verifying the presence of an object property using a variable can be a common task. However, directly using the variable as the property name leads to undefined results.

Example:

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

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

To overcome this, one must utilize methods that explicitly check property existence.

Solutions:

Option 1: hasOwnProperty

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

Option 2: in operator (checks for both direct and inherited properties)

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

Option 3: Direct in operator usage (checks only for direct properties)

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

Note: hasOwnProperty does not check inherited properties, while the in operator does.

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