SOLVED: How do I access functions on the "Window" object from JavaScript running in ClearScript?

[PoseidonEnergy]

When running JavaScript in a browser, there is a global window object that provides a number of helpful (also global) functions, including:

atob
decodeURI
isNaN
eval

Normally you can just write the following JavaScript in a browser with no errors:

const x = isNaN("hello"); // true

However, the isNaN function is unavailable to JavaScript running in ClearScript, meaning the code above does not work.

Is there something I can do to make those standard window functions available to me in ClearScript? I realize that technically I could expose a host object with all those same functions ported to C#, but I'm hoping there's a switch or something I can set that would be fast and easy. I also know that window in the context of ClearScript doesn't make sense, but I am just looking for the functions. I don't care if window.document is null.

[DavidBal]

Hi @PoseidonEnergy,

yes there is a way to do this, you need to provide the function your self.

Here are a example how i am doing it for atob, btoa and isNaN:

private void Patch(V8ScriptEngine scriptEngine)
{
    string jsPatch = """
        if(typeof(btoa) !== "function")
        {
            globalThis.btoa = (stringToEncode) => {
                const b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
                stringToEncode = String(stringToEncode);
                const rest = stringToEncode.length % 3;
                let result = "";
                for (let i = 0; i < stringToEncode.length;) {
                    const a = stringToEncode.charCodeAt(i++);
                    if (a > 255) {
                        throw new TypeError(`Fehler beim Ausführen von 'btoa': Der String der Encoded werden soll enthält ein ungültiges Zeichen (Position: ${i - 1}), diese liegt aushalb von 'Latin1'.`);
                    }
                    const b = stringToEncode.charCodeAt(i++);
                    if (b > 255) {
                        throw new TypeError(`Fehler beim Ausführen von 'btoa': Der String der Encoded werden soll enthält ein ungültiges Zeichen (Position: ${i - 1}), diese liegt aushalb von 'Latin1'.`);
                    }
                    const c = stringToEncode.charCodeAt(i++);
                    if (c > 255) {
                        throw new TypeError(`Fehler beim Ausführen von 'btoa': Der String der Encoded werden soll enthält ein ungültiges Zeichen (Position: ${i - 1}), diese liegt aushalb von 'Latin1'.`);
                    }
                    const bitmap = (a << 16) | (b << 8) | c;
                    result += b64.charAt(bitmap >> 18 & 63) + b64.charAt(bitmap >> 12 & 63) + b64.charAt(bitmap >> 6 & 63) + b64.charAt(bitmap & 63);
                }
                return rest ? result.slice(0, rest - 3) + "===".substring(rest) : result;
            };
        }

        if (typeof atob !== 'function')
        {
            globalThis.atob = (string) =>
            {
                const b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
                const b64re = /^(?:[A-Za-z\d+\/]{4})*?(?:[A-Za-z\d+\/]{2}(?:==)?|[A-Za-z\d+\/]{3}=?)?$/;
                // atob can work with strings with whitespaces, even inside the encoded part,
                // but only \t, \n, \f, \r and ' ', which can be stripped.
                string = String(string).replace(/[\t\n\f\r ]+/g, "");
                if (!b64re.test(string))
                    throw new TypeError("Failed to execute 'atob' on 'Window': The string to be decoded is not correctly encoded.");
                
                // Adding the padding if missing, for semplicity
                string += "==".slice(2 - (string.length & 3));
                let bitmap, result = "", r1, r2, i = 0;
                for (; i < string.length;)
                {
                    bitmap = b64.indexOf(string.charAt(i++)) << 18 | b64.indexOf(string.charAt(i++)) << 12
                        | (r1 = b64.indexOf(string.charAt(i++))) << 6 | (r2 = b64.indexOf(string.charAt(i++)));
                
                    result += r1 === 64 ? String.fromCharCode(bitmap >> 16 & 255)
                        : r2 === 64 ? String.fromCharCode(bitmap >> 16 & 255, bitmap >> 8 & 255)
                            : String.fromCharCode(bitmap >> 16 & 255, bitmap >> 8 & 255, bitmap & 255);
                }
                return result;
            };
        }

        if(typeof isNaN !== 'function')
        {
            globalThis.isNaN = (num) =>{
                return Number.isNaN(num);
            }
        }
                

        """;

    scriptEngine.Evaluate(jsPatch);
}

You need to execute this code before running your script.

I hope this helps.

Kind regards,
David

[PoseidonEnergy]

Thanks, that worked. I did it slightly different however--I simply checked if globalThis.window is null and created a fake global Window object to store everything. Like this for example:

(() => {
    if (globalThis.window == null) {
        const makeFakeElement = () => ({
            innerHTML: "",
            appendChild: elem => elem
        });
        const fakeWindow = {
            location: {
                origin: ""
            },
            document: {
                cookie: "",
                head: makeFakeElement(),
                createElement: () => makeFakeElement(),
                addEventListener: () => undefined
            },
            isNaN: num => Number.isNaN(num),
            addEventListener: () => undefined,
        };
        Object.assign(globalThis, fakeWindow);
        globalThis.window = globalThis;
    }
})();