React-Native : How to get callback of api call in another class - reactjs

Question

I am calling a web service
Here is my code:
var result;
export function callPostApi(urlStr, params)
{
fetch(urlStr, {method: "POST", headers: {
'Accept': 'application/json',
'Content-Type': 'application/json',
},
body: JSON.stringify(params)})
.then((response) => response.json())
.then((responseData) => {
result = JSON.stringify(responseData)
})
.catch((error) => { console.error(error);
Alert.alert('Alert Title failure' + JSON.stringify(error))
})
.done();
return result
}
I am calling from here:
callapi(){
var dict = {
email: 'at#gmail.com',
password: '123456',
}
result = callPostApi('http://demo.com', dict)
}
Currently, it is calling in Async mode that we want but code is written below this method getting execute immediately after calling of above method
i want callback when result from sever has received so that i can execute code written below the above method is execute after receiving response from server.

Answer 1

You need to use Promises.
Change your callPostApi function to return a Promise, then you can chain additional then, catch and finally calls.
export function callPostApi(urlStr, params) {
return fetch(urlStr, {
method: "POST",
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json',
},
body: JSON.stringify(params)
})
.then((response) => response.json())
.then((responseData) => {
result = JSON.stringify(responseData)
})
.catch((error) => {
console.error(error);
Alert.alert('Alert Title failure' + JSON.stringify(error))
});
}
callapi() {
callPostApi('http://demo.com', {
email: 'at#gmail.com',
password: '123456',
})
.then((response) => {
// Continue your code here...
});
}