const SLOW_LOAD_TIME = 1500;

function waitOrLoad(callbackIfSlow, maximumLoadTime = SLOW_LOAD_TIME) {
    const timeout = setTimeout(callbackIfSlow, maximumLoadTime);
    return function loadingFinished() {
        clearTimeout(timeout);
    }
}

async function doSomething() {
    const loadingFinished = waitOrLoad(() => {
         console.log('loading is slow'); 
    });
    // do something that the user expects to take some time, e.g. loading data ...
    loadingFinished();
}