How Can I Programmatically List Browser-Available Fonts in JavaScript?

List Available Fonts for User Selection in Browser

Problem:

In web development, one may encounter the need to offer users a dropdown list of fonts that their browser can display. How can you programmatically obtain this list in JavaScript, without relying on hardcoded or server-fetched data?

Solution:

Detecting Fonts with JavaScript

Fortunately, JavaScript provides a means to detect the fonts available on a user's system. The following snippet can be implemented:

var detector = new Detector();

// Function to detect if a font is available
function detectFont(font) {
  return detector.detect(font);
}

// Get the list of detected fonts
var availableFonts = [];
for (var font in detector.detectFonts()) {
  if (detectFont(font)) {
    availableFonts.push(font);
  }
}

console.log(availableFonts);

This will log an array of all the fonts that the browser can display.

Code Explanation

The Detector class uses a technique called "font fingerprinting" to compare a specific font against a set of base fonts and determine if it is available. This is achieved by measuring the width and height of the text rendered in the font and comparing it to the measurements of the text rendered in the base fonts. If the measurements differ, it indicates the presence of the specific font.

Additional Information

The font detection method can be further improved using additional approaches, such as checking for font files in the system or using Flash or Canvas to render text. However, these methods are not as reliable as JavaScript's native font detection.

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