opencv/modules/js/src/loader.js

async function loadOpenCV(paths, onloadCallback) {
    let OPENCV_URL = "";
    let asmPath = "";
    let wasmPath = "";
    let simdPath = "";
    let threadsPath = "";
    let threadsSimdPath = "";

    if(!(paths instanceof Object)) {
        throw new Error("The first input should be a object that points the path to the OpenCV.js");
    }

    if ("asm" in paths) {
        asmPath = paths["asm"];
    }

    if ("wasm" in paths) {
        wasmPath = paths["wasm"];
    }

    if ("threads" in paths) {
        threadsPath = paths["threads"];
    }

    if ("simd" in paths) {
        simdPath = paths["simd"];
    }

    if ("threadsSimd" in paths) {
        threadsSimdPath = paths["threadsSimd"];
    }

    let wasmSupported = !(typeof WebAssembly === 'undefined');
    if (!wasmSupported && OPENCV_URL === "" && asmPath != "") {
        OPENCV_URL = asmPath;
        console.log("The OpenCV.js for Asm.js is loaded now");
    } else if (!wasmSupported && asmPath == ""){
        throw new Error("The browser supports the Asm.js only, but the path of OpenCV.js for Asm.js is empty");
    }

    let simdSupported = wasmSupported ? await wasmFeatureDetect.simd() : false;
    let threadsSupported = wasmSupported ? await wasmFeatureDetect.threads() : false;

    if (simdSupported && threadsSupported && threadsSimdPath != "") {
        OPENCV_URL = threadsSimdPath;
        console.log("The OpenCV.js with simd and threads optimization is loaded now");
    } else if (simdSupported && simdPath != "") {
        if (threadsSupported && threadsSimdPath === "") {
            console.log("The browser supports simd and threads, but the path of OpenCV.js with simd and threads optimization is empty");
        }
        OPENCV_URL = simdPath;
        console.log("The OpenCV.js with simd optimization is loaded now.");
    } else if (threadsSupported && threadsPath != "") {
        if (simdSupported && threadsSimdPath === "") {
            console.log("The browser supports simd and threads, but the path of OpenCV.js with simd and threads optimization is empty");
        }
        OPENCV_URL = threadsPath;
        console.log("The OpenCV.js with threads optimization is loaded now");
    } else if (wasmSupported && wasmPath != "") {
        if(simdSupported && threadsSupported) {
            console.log("The browser supports simd and threads, but the path of OpenCV.js with simd and threads optimization is empty");
        }

        if (simdSupported) {
            console.log("The browser supports simd optimization, but the path of OpenCV.js with simd optimization is empty");
        }

        if (threadsSupported) {
            console.log("The browser supports threads optimization, but the path of OpenCV.js with threads optimization is empty");
        }

        OPENCV_URL = wasmPath;
        console.log("The OpenCV.js for wasm is loaded now");
    } else if (wasmSupported) {
        console.log("The browser supports wasm, but the path of OpenCV.js for wasm is empty");

        if (asmPath != "") {
            OPENCV_URL = asmPath;
            console.log("The OpenCV.js for Asm.js is loaded as fallback.");
        }
    }

    if (OPENCV_URL === "") {
        throw new Error("No available OpenCV.js, please check your paths");
    }

    let script = document.createElement('script');
    script.setAttribute('async', '');
    script.setAttribute('type', 'text/javascript');
    script.addEventListener('load', () => {
        onloadCallback();
    });
    script.addEventListener('error', () => {
        console.log('Failed to load opencv.js');
    });
    script.src = OPENCV_URL;
    let node = document.getElementsByTagName('script')[0];
    if (node.src != OPENCV_URL) {
        node.parentNode.insertBefore(script, node);
    }
}