Why does element.style.display return an empty string when styles are defined in CSS?

Understanding the Behavior of element.style Property in JavaScript

The element.style property in JavaScript behaves differently when you define styles in CSS versus setting them directly through the element's style attribute.

When you assign styles in CSS, element.style returns an empty string for properties like display. This is because the element doesn't have any inline styles applied, and the style property in CSS overrides any inline styles.

However, if you set the style property directly through the element, element.style will return the value you set.

Reason for the Empty Display Property

The reason for the empty display property in CSS is that the element's display property is inherited from its parent element or the default CSS style rules. In the example provided, the display property is set to block in the CSS, but the element itself doesn't explicitly set the display property.

Therefore, when you access the element.style.display property, it returns an empty string because there's no inline style applied to the element and the inherited style from the CSS is not accessible through element.style.

Retrieving Styles Applied by CSS

If you need to retrieve the styles applied by CSS, you can use the window.getComputedStyle() method. This method returns an object that represents the computed style values for an element, including styles inherited from parent elements and applied through cascading style sheets.

For example:

const displayValue = window.getComputedStyle(document.getElementById('test')).display;

In this case, displayValue will contain the "block" value as specified in the CSS, even though element.style.display returns an empty string.

Inline CSS vs. External CSS

While inline CSS is not considered good practice for code modularity and maintainability, you should still be aware of the different behaviors of inline and external styles when working with the element.style property.

By understanding this behavior, you can accurately retrieve or modify styles in JavaScript applications and effectively separate the concerns of HTML, CSS, and JavaScript code.

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