So, I wrote the following function:
function getData() {
var data;
$(function () {
$.getJSON('https://ipinfo.io', function (ipinfo) {
data = ipinfo;
console.log(data);
})
})
console.log(data);
}
The problem with the above is the 2nd console.log doesn't retain the info from the assignment inside the jQuery and logs an undefined object. I'm not exactly sure what is wrong, but I believe it to be something quite minor. However, as much as I've searched online, I haven't found an answer for this particular problem.
One line: Javascript is Asynchronous.
While many struggle to figure out what it exactly means, a simple example could possibly explain you that.
For a conventional programmer, it is very hard to grasp that the order of execution in case of JavaScript will not be 1,2 and then 3 but rather 1,3,2.
Why this happens is because of Javascript's event-loop mechanism where each asynchronous action is tied with an event and callbacks are called only when the event occurs. Meanwhile, the code outside the callback function executes without holding on for the event to actually occur.
In your case:
var data;
$(function () {
$.getJSON('https://ipinfo.io', function (ipinfo) {//async function's callback
data = ipinfo;
console.log(data);//first console output
})
})
console.log(data);//second console output
While the async function's callback is executed when the data is received from the $.getJSON
function, javascript proceeds further without waiting for the callback
to assign the value to the data
variable, causing you to log undefined
in the console (which is the value of the data
variable when you call console.log
.
I hope I was able to explain that.!
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