How can you reliably determine if a JavaScript object is a DOM element?

How to Determine if a JavaScript Object is a DOM Object

When working with JavaScript, it is often necessary to determine if an object represents a DOM (Document Object Model) element. This distinction is crucial for handling user interactions, manipulating page elements, and ensuring proper functionality.

One common approach involves checking if the object has a tagName property. However, this method is fallible, as it assumes that DOM elements always possess this property. To fully address this issue, a more robust solution is required.

Suggested Solutions

One alternative is to leverage the W3 DOM2 specification, which provides the instanceof HTMLElement check. This approach works well in browsers such as Firefox, Opera, and Chrome.

For browsers that do not support W3 DOM2, a more comprehensive approach is recommended:

function isElement(obj) {
  try {
    return obj instanceof HTMLElement;
  } catch(e) {
    return (typeof obj === "object") &&
      (obj.nodeType === 1) &&
      (typeof obj.style === "object") &&
      (typeof obj.ownerDocument === "object");
  }
}

This code tests for properties common to all DOM elements, ensuring a reliable determination.

Alternative Implementations

Another approach is to define separate functions for both DOM nodes and DOM elements:

function isNode(o) {
  return (
    typeof Node === "object" ? o instanceof Node :
    o && typeof o === "object" && typeof o.nodeType === "number" && typeof o.nodeName==="string"
  );
}

function isElement(o) {
  return (
    typeof HTMLElement === "object" ? o instanceof HTMLElement :
    o && typeof o === "object" && o !== null && o.nodeType === 1 && typeof o.nodeName==="string"
  );
}

These functions provide a more refined check, catering to specific requirements for both nodes and elements within the DOM.

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