json.ts

/**
 * A wrapper to work around otherwise not being able to mutate caller's string.
 */
class WrappedValue {
    constructor(public val: any) {}
}

function strip_out_nuls_(wrapped: WrappedValue): number {
    let had_nul = 0;
    const val = wrapped.val;
    if (typeof val === "string" && val.includes("\u0000")) {
        wrapped.val = val.replaceAll("\u0000", "");
        had_nul = 1;
    } else if (typeof val === "object" && val !== null) {
        for (const [key, obj_val] of Object.entries(val)) {
            const wrapped = new WrappedValue(obj_val);
            had_nul |= strip_out_nuls_(wrapped);
            (val as any)[key] = wrapped.val;
        }
    } else if (Array.isArray(val)) {
        for (let idx = 0; idx < val.length; idx++) {
            const wrapped = new WrappedValue(val[idx]);
            had_nul |= strip_out_nuls_(wrapped);
            val[idx] = wrapped.val;
        }
    }
    return had_nul;
}

// Recursively walk a deserialized JSON object and replace strings (except object keys)
// to strip out all NUL characters. Returns `true` if any NUL was removed.
function strip_out_nuls(val: any): boolean {
    return Boolean(strip_out_nuls_(new WrappedValue(val)));
}

{
    let obj = {"hello": 3, "world": ["val\u0000thing", "\u0000", {"hello": "\u0000\u0000"}]};
    console.log(obj);
    let had_nul = strip_out_nuls(obj);
    console.log(had_nul, obj);
}

{
    let obj = {"hello": 3};
    console.log(obj);
    let had_nul = strip_out_nuls(obj);
    console.log(had_nul, obj);
}

Improvements or rewrites welcome