How to return a JSON in GET method?

Question

Based on xlsx github documentation, i made this function to return a json object. This is a method i tried:

function getData(){
 var data; 
 var url = "Book1.xlsx";
 var req = new XMLHttpRequest();
 req.open("GET", url, true);
 req.responseType = "arraybuffer";
 req.onload = function(e) {
 var data = new Uint8Array(req.response);
 var wb = XLSX.read(data, {type:"array"});
 var ws = wb.Sheets['Sheet1'];
 data = XLSX.utils.sheet_to_json(ws);
 //console.log(data);
 }
 //return data;
 req.send();
}

My question is how can i return data so that i'll be able to use it in my other function? My problem is i have a lot of XMLHttpRequest() just to read my Book1.xlsx. Hope someone can help.

• Tân: Does this answer your question? Callback function example
• Tân: Dup: Calling a callback in javascript
• Tân: Dup: Create a custom callback in JavaScript
• Alexander Paudak: How does this callback works?

Answer 1

function getData(cb){
 var data; 
 var url = "Book1.xlsx";
 var req = new XMLHttpRequest();
 req.open("GET", url, true);
 req.responseType = "arraybuffer";
 req.onload = function(e) {
 var data = new Uint8Array(req.response);
 var wb = XLSX.read(data, {type:"array"});
 var ws = wb.Sheets['Sheet1'];
 data = XLSX.utils.sheet_to_json(ws);
 cb(data)
 //console.log(data);
 }
 //return data;
 req.send();
}
const d = new Promise(resolve =>
 getData(resolve)
) 
d.then(data => { 
 console.log(data) 
})

• Alexander Paudak: Thank you very much sir. Is Promise a built in function in JavaScript?
• syarul: yep @AlexanderPaudak