Given the following examples, why is outerScopeVar
undefined in all cases?
var outerScopeVar;
var img = document.createElement('img');
img.onload = function() {
outerScopeVar = this.width;
};
img.src="https://stackoverflow.com/questions/23667086/lolcat.png";
alert(outerScopeVar);
var outerScopeVar;
setTimeout(function() {
outerScopeVar="Hello Asynchronous World!";
}, 0);
alert(outerScopeVar);
// Example using some jQuery
var outerScopeVar;
$.post('loldog', function(response) {
outerScopeVar = response;
});
alert(outerScopeVar);
// Node.js example
var outerScopeVar;
fs.readFile('./catdog.html', function(err, data) {
outerScopeVar = data;
});
console.log(outerScopeVar);
// with promises
var outerScopeVar;
myPromise.then(function (response) {
outerScopeVar = response;
});
console.log(outerScopeVar);
// geolocation API
var outerScopeVar;
navigator.geolocation.getCurrentPosition(function (pos) {
outerScopeVar = pos;
});
console.log(outerScopeVar);
Why does it output undefined
in all of these examples? I don’t want workarounds, I want to know why this is happening.
Note: This is a canonical question for JavaScript asynchronicity. Feel free to improve this question and add more simplified examples which the community can identify with.