If you want to mock an API response in Javascript use Promise with setTimeout inside the function that will perform the call to the API like so:

return new Promise((resolve) => {
    setTimeout(() => {
        resolve(//insert what a successful response would be);
    }, 2000);
});

We can also mock failing:

return new Promise((resolve, reject) => {
    setTimeout(() => {
        if(condition) {
            resolve(//insert what a successful response would be);
        }
        else{
            reject(//insert what an error response would be);
        }
    }, 2000);
})