Why Does a JavaScript Function Name Clashing with an Element ID Cause Errors?

Why JS Function Name Conflicts with Element ID

Introduction

When defining a JavaScript function with the same name as an element's ID, unexpected errors can occur. This article investigates the underlying reason for this conflict and explores any JavaScript specifications or restrictions regarding such situations.

Explanation

JavaScript has a legacy scope chain issue that stems from its early versions (1.0 to 1.3). In the event handler attribute value of a form control that is part of a form, the Form object representing the form becomes accessible as a second-next object in the scope chain, while the form control object itself is the second-next.

The Form object possesses properties representing the names of its contained form controls. This allows accessing a form control object using the following syntax:

myForm.border

This is a shorthand for the standards-compliant syntax:

document.forms["myForm"].elements["border"]

As a result, when using a form control's name in an event-handler attribute value, it is equivalent to referencing the corresponding property of the Form object. If this form control's name matches a user-defined function, it leads to the execution of the form control object, which is not callable. This causes the error "TypeError: [function name] is not a function."

Impact of DOM Level 2 HTML Specification

DOM Level 2 HTML Specification, which standardized existing DOM implementations, introduced additional features. It specified that items of HTMLCollections can be accessed by either name or ID using the bracket property accessor syntax [...].

In the context of forms and form controls, this extended the access method to include elements with IDs as well. Consequently, the aforementioned conflict became applicable to elements with IDs, resulting in the same error when the function name conflicts with the element's ID.

Conclusion

Understanding this legacy issue requires knowledge of JavaScript's historical evolution and its influence on the DOM API. Adhering to best practices, such as avoiding naming conflicts between form controls and functions or using IDs, can mitigate this issue and prevent unexpected errors.

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