third_party/rust_crates/tiny_mirrors/ttf-parser/examples/wasm/index.html

<h2>ttf-parser in WebAssembly</h2>
<p><small>(supports font files drag and drop)</small></p>
<p><span id="fileName">TTC.ttc</span>:</p>
<p><code>ttfp_fonts_in_collection():</code> <code id="fontsInCollection"></code></p>
<p><code>ttfp_is_variable():</code> <code id="isVariable"></code></p>
<p><code>ttfp_get_weight():</code> <code id="fontWeight"></code></p>
<script>
'use strict';

let wasm;

function update(fontBlob) {
    const exports = wasm.instance.exports;

    // How our heaped is structured, as ttf-parser doesn't allocate anything
    // it is all ours and we can decide how to use it
    const heapStart = exports.__heap_base.value;
    const fontHandlerAddress = heapStart;
    const fontHandlerLength = exports.ttfp_face_size_of();
    const fontDataAddress = heapStart + fontHandlerLength;
    const fontDataLength = fontBlob.length;

    // Copy the fetched blob into WebAssembly machine
    const heapu8 = new Uint8Array(exports.memory.buffer);
    heapu8.set(fontBlob, fontDataAddress);

    fontsInCollection.textContent = exports.ttfp_fonts_in_collection(fontDataAddress, fontDataLength);

    // Create font handler
    exports.ttfp_face_init(fontDataAddress, fontDataLength, 0/*face index*/, fontHandlerAddress);

    isVariable.textContent = exports.ttfp_is_variable(fontHandlerAddress);
    fontWeight.textContent = exports.ttfp_get_weight(fontHandlerAddress);
}

fetch('ttfparser.wasm').then(x => x.arrayBuffer()).then(WebAssembly.instantiate).then(result => {
    wasm = result;
    // Extend wasm machine heap once now that we are here, each page is 64kb
    wasm.instance.exports.memory.grow(400);

    // Could be done in parallel using Promise.all
    fetch('TTC.ttc').then(x => x.arrayBuffer()).then(result => {
        update(new Uint8Array(result));
    });
});

document.addEventListener('dragover', e => {
    e.stopPropagation(); e.preventDefault();
}, false);
document.addEventListener('dragleave', e => {
    e.stopPropagation(); e.preventDefault();
}, false);
document.addEventListener('drop', e => {
    e.stopPropagation(); e.preventDefault();
    handleFontUpdate(e.dataTransfer.files[0]);
});
// document.addEventListener('paste', e => {
//     handleFontUpdate(e.clipboardData.files[0]);
// });
function handleFontUpdate(file) {
    if (!file) return;
    fileName.textContent = file.name;
    const reader = new FileReader();
    reader.addEventListener('load', () => update(new Uint8Array(reader.result)));
    reader.readAsArrayBuffer(file);
}
</script>