How Can I Determine the Font Actually Used by a User\'s Browser?

Determining the Utilized Font in a Web Page

In web design, specifying multiple fonts in CSS provides fallback options for browsers that may not have the primary font installed. Identifying the actual font used by the user's browser can be crucial for specific applications.

Detecting Font Utilization

To detect which of the defined fonts is used, you can utilize a technique that involves comparing the width of a rendered string using the target font and the derived font. Here's how it works:

1. Define an element with a specific font (e.g., Calibri).
2. Set a string of text to the element.
3. Measure the width of the rendered string.
4. Repeat the process using a generic font (e.g., "sans-serif").

If the measured widths match the expected width for the target font, it is likely that the target font is available on the user's system. Conversely, if the widths differ, the target font is likely not installed.

Note:

This approach may not be entirely reliable for monospaced fonts, which have fixed character widths. Additionally, it's important to ensure that CSS rules don't affect the element's styling during the measurement process.

This technique enables developers to detect whether a specific font is present on the user's browser, allowing for conditional display of content or features that rely on the presence of the font.

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