How pass optionnal parameter in a function in App Service


I have the code below. I want to be able to add optional parameter to the query (path), like ?itemPerPage=500 but when I add that, it does’nt work.

exports = async function (projid, projName, username, password) {

    const arg = {
        scheme: 'https',
        host: '',
        path: 'api/atlas/v1.0/groups/' + projid + '/events/?itemPerPage=500',
        username: username,
        password: password,
        headers: {
            'Content-Type': ['application/json'], 'Accept-Encoding': ['bzip, deflate']
        digestAuth: true,
    // The response body is a BSON.Binary object. Parse it and return.
    response = await context.http.get(arg);