How to increase the range of an array taken from an API query - react-native

Question

I have a function for when clicking a button increase the contents of a list.
Content is removed from an API by the following code:
const [data, setData] = useState();
const [maxRange, setMaxRange] = useState(2);
const getAPIinfo = ()=>{
GetEvents(maxRange, 0).then((response) => response.json())
.then(result_events => {
const events = result_events;
setData({events:events});
}).catch(e => setData({events:events}));
}
And my function is this:
const buttonLoadMore = ({data,type}) =>{
setMaxRange(prevRange => prevRange + 4);
data = data.slice(0,maxRange);
}
what I'm not able to do is update the maxRange value of the API query to increase the list...

Answer 1

this function should be heavily refactored:
const buttonLoadMore = ({data,type}) =>{
setMaxRange(prevRange => prevRange + 4);
data = data.slice(0,maxRange);
}
when you use maxRange here, you are setting new state, while the function itself ir running, the state is not instantly updated, buttonLoadMore is a function in a particular time. it cannot get new maxRange instantly, while running buttonLoadMore does that make sense? Also you cannot update data state just like a regular variable by assigning new variable using = operator, you should refactor this function to something like this:
const buttonLoadMore = ({data})=> {
const newMaxRange = maxRange + 4;
setMaxRange(newMaxRange);
const newData = {events: [...data.events.slice(0, newMaxRange)]};
setData({...newData})
}
also you will get bug here. since your getAPIinfo is setting data state to an object {events: events}. I took the liberty and tried refactoring it here.
There is also a bug in your getAPIinfo in line }).catch(e => setData({events:events})); the events variable you declared in .then function cannot be reached here. It is simply out of scope. unless you know that .catch resolves into data, you will get an error in this line.
take a look at this example here:
const promiseFunction = ()=>{
return new Promise<string>((resolve)=>resolve('i like coca cola'))
}
const getter = () => {
promiseFunction()
.then(response => {
const thenVariable = response;
console.log(thenVariable) // i like coca cola
})
.catch(error=>{
console.log(thenVariable) // Error:Cannot find name 'thenVariable'.
})
}
as you can see .catch() is in different scope than .then() will not be available outside so events cannot be reached by .catch function.
Usually you would use catch for error handling. Maybe show a line on screen, that error has accoured, and data cannot be fetched at this time. etc. There's a very good book that explains all these concepts in detail here: https://github.com/getify/You-Dont-Know-JS
I would strongly recommend for you to switch to typescript because your code is crawling with bugs that should be easily avoided just by type checking, and adding eslint configurations.