async WebAssembly.Function polyfill

wasmfunc.polyfill.js

// For Firefox or other browsers that don't provide WebAssembly.Function APIs,
// this polyfill, albeit async, can be used as a substitute.
//
// Using WASM, this polyfill is accepted by WebAssembly.Tables, and can be inserted
// into them without failure
if (!WebAssembly.Function) {
    const vu32 = (x) => {
        let out = [];
        do {
            let byte = x & 0x7F;
            x >>= 7;
            if (x) byte |= 0x80
            out.push(byte);
        } while (x);

        return out;
    }

    const deepFlat = arr => arr.flatMap(e => Array.isArray(e) ? deepFlat(e.flat()) : e);
    const vector = (arr) => vu32(arr.length).concat(deepFlat(arr));
    const string = (str) => vector(Array.from(new TextEncoder().encode(str)))
    const types = {
        "i32": 0x7F,
        "i64": 0x7E,
        "f32": 0x7D,
        "f64": 0x7C,
        "v128": 0x7B,
        "funcref": 0x70,
        "externref": 0x6F
    }

    class WebAssemblyFunction {
        constructor({ parameters, results }, callable) {
            return new Promise(async (resolve, reject) => {
                for (let i = 0; i < parameters.length; ++i) {
                    if (!types.hasOwnProperty(parameters[i])) {
                        return reject(new TypeError(`Argument 0 parameter type at index #${i} must be a value type`));
                    }
                }

                for (let i = 0; i < results.length; ++i) {
                    if (!types.hasOwnProperty(results[i])) {
                        return reject(new TypeError(`Argument 0 result type at index #${i} must be a value type`));
                    }
                }

                if (typeof callable !== "function") {
                    return reject(new TypeError("Argument 1 must be a function"));
                }

                const w = await WebAssembly.instantiate(new Uint8Array(deepFlat([
                    [0x00, 0x61, 0x73, 0x6d], // magic
                    [0x01, 0x00, 0x00, 0x00], // version
                    [
                        0x1, // type section
                        vector(deepFlat(vector([
                            [
                                0x60,
                                vector(parameters.map(n => types[n])),
                                vector(results.map(n => types[n]))
                            ]
                        ])))
                    ],
                    [
                        0x2, // import section
                        vector(deepFlat(vector([
                            [
                                string("m"),
                                string("c"),
                                0,
                                vu32(0)
                            ]
                        ])))
                    ],
                    [
                        0x3, // function section
                        vector(deepFlat(vector([
                            [
                                vu32(0)
                            ]
                        ])))
                    ],
                    [
                        0x7, // export section
                        vector(deepFlat(vector([
                            [
                                string("e"),
                                0,
                                vu32(1)
                            ]
                        ])))
                    ],
                    [
                        0xA, // function section
                        vector(deepFlat(vector([
                            vector(deepFlat([
                                vector([]),

                                ...parameters.flatMap((_,i) => [0x20, ...vu32(i)]),
                                0x10, vu32(0), // call $0
                                0x0B // end
                            ]))
                        ])))
                    ],
                ])), { m: { c: callable } });

                resolve(w.instance.exports.e.bind());
            });
        }
    }

    WebAssembly.Function = WebAssemblyFunction;
}