Why Does JavaScript Display '[object Object]' When Returning an Object?

What is the Meaning of "[object Object]"?

When attempting to display the return value of a function using an alert box, you may encounter the enigmatic message "[object Object]". Delving into the JavaScript code behind this scenario reveals the following:

function whichIsVisible() {
  if (!.is(':hidden')) return ;
  if (!.is(':hidden')) return ;
}

Understanding the Error

The error arises because the whichIsVisible() function is attempting to return a jQuery object, which is a type of JavaScript object. Without specifying the object's type, JavaScript defaults to "Object" when converting it to a string.

Unveiling the Object Prototype

The Object prototype provides methods for manipulating and interrogating objects. One such method is toString(), which returns a string representation of the object. In the case of a generic object, toString() simply returns "[object Object]".

Distinguishing Between Object Types

It is important to note that "object" in JavaScript encompasses a wider range of data structures beyond simple key-value pairs. These include:

• Function objects: [object Function]
• Array objects: [object Array]
• RegExp objects: [object RegExp]
• Date objects: [object Date]

Identifying Object Objects

While the term "object" in JavaScript is often synonymous with "Object objects," these objects have a specific constructor function named "Object."

Example: Exploring Object Types

The following example illustrates how different object types are serialized in JavaScript:

function stringify(x) {
  console.log(Object.prototype.toString.call(x));
}

stringify({}); // "[object Object]"
stringify([]); // "[object Array]"
stringify(function() {}); // "[object Function]"
stringify(new Date()); // "[object Date]"

Conclusion

In JavaScript, "[object Object]" indicates a generic object. Understanding the different types of objects and their unique string representations is crucial for effectively handling their serialized values.

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