How Can I Detect the Font Actually Rendered in a User\'s Browser?

Detecting Utilized Fonts on a Web Page

Identifying Rendered Fonts

Suppose you have a CSS rule determining the font family of your web page. How can you discern which font is actually used in the user's browser? This question becomes pertinent when specific glyphs are not present in certain fonts, demanding the display of a download link for correct glyph rendering.

Measuring Rendered Strings

One approach involves setting an element with a specific font and assigned string. If the font does not exist in the user's system, the element adopts the font of its parent. By measuring the width of the rendered string, you can determine if the expected font or its derived counterpart is being used. This method, however, does not work for monospaced fonts.

Derivation

This approach was popularized by the Javascript/CSS Font Detector article on ajaxian.com, published in March 2007.

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