What option to make difference between object & array about flat HOT 1 OPEN

function flatten(object: any): { [key: string]: any } {
    const output: any = {};

    function step(object: any, prev?: any, currentDepth?: number, useBrackets?: boolean) {
        const depth = currentDepth || 1;
        Object.keys(object).forEach(function (key) {
            const value = object[key];
            const isarray = Array.isArray(value);
            const type = Object.prototype.toString.call(value);
            const isobject = type === '[object Object]' || type === '[object Array]';

            const newKey = prev
                ? `${prev}${useBrackets ? '[' : '.'}${key}${useBrackets ? ']' : ''}`
                : key;

            if (isobject && Object.keys(value).length) {
                return step(value, newKey, depth + 1, isarray);
            }

            output[newKey] = value;
        });
    }

    step(object);

    return output;
}