Why is Accessing DOM Elements via Global Properties Discouraged?

Global Properties and DOM Tree Elements with IDs

In web browsers like Internet Explorer and Chrome, elements in the DOM tree with assigned IDs can be accessed through the global object using their ID as a variable name or a property of the window object. For instance, an element with the ID "example" can be obtained using:

alert(example.innerHTML); // Alerts "some text".

or

alert(window["example"].innerHTML); // Alerts "some text".

However, this behavior is discouraged for several reasons:

• Clashing with Native Properties: Named elements become properties of the document object, which can conflict with its actual properties. IE further compounds this by also adding named elements as properties of the window object, potentially colliding with existing members.
• Global Scope Visibility: These elements become visible as global-like variables. While real global variables shadow them in code, omitting the var declaration in assignments to global variables with clashing names can inadvertently alter the element's value.
• Lack of Support Across Browsers: Only IE, Chrome, and Opera initially supported this behavior, making it inconsistent across different platforms.
• Deprecation in HTML5: The HTML5 specification has standardized this behavior, extending it to Firefox. However, it is still considered bad practice to rely on named elements being visible on window or as globals.

Instead, it is preferable to use the standardized getElementById method for retrieving elements from the DOM tree, as it is widely supported and less ambiguous.

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