How Can JavaScript Detect Available Fonts for User Font Selection?
Nov 27, 2024 am 10:49 AM
Detecting Supported Fonts for User Customization
Question:
How to use JavaScript to get the browser A list of all fonts that can be displayed to provide font selection functionality to the user?
Answer:
Lalit Patel's JavaScript font detection library: http://www.lalit.org/lab/javascript-css-font-detect
Code:
/**
* Detector JavaScript code to identify available fonts in a browser.
*/
var Detector = function() {
// Base fonts for comparison against candidate fonts
var baseFonts = ['monospace', 'sans-serif', 'serif'];
// Test string with characters of varying widths and heights
var testString = "mmmmmmmmmmlli";
// Test font size
var testSize = '72px';
// Append a SPAN element to the body for font width measurement
var s = document.createElement("span");
s.style.fontSize = testSize;
s.innerHTML = testString;
var defaultWidth = {}, defaultHeight = {};
// Calculate default widths for base fonts
for (var index in baseFonts) {
s.style.fontFamily = baseFonts[index];
document.body.appendChild(s);
defaultWidth[baseFonts[index]] = s.offsetWidth;
defaultHeight[baseFonts[index]] = s.offsetHeight;
document.body.removeChild(s);
}
function detect(font) {
var detected = false;
// Compare candidate font's width and height against base fonts
for (var index in baseFonts) {
s.style.fontFamily = font + ',' + baseFonts[index]; // Fallback to base font
document.body.appendChild(s);
var matched = (s.offsetWidth != defaultWidth[baseFonts[index]] || s.offsetHeight != defaultHeight[baseFonts[index]]);
document.body.removeChild(s);
detected = detected || matched;
}
return detected;
}
this.detect = detect;
};
How it Works:
This library analyzes character width and height differences between different fonts. Each character's appearance varies across fonts, resulting in unique widths and heights for the same test string. By comparing a candidate font against three base fonts, the library can determine whether the candidate font is available in the browser.
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