getElementId function:
function getIdElements(idname, callback) {
callback(document.getElementById(idname))
};
I want to use it like this but plLen gets undefined:
var plLen = getIdElements("length", function(e){return e.textContent});
I would love if someone could explain it as deep as possible. Thank you.
You can simply return the value the callback returns:
function getIdElements(idname, callback) {
return callback(document.getElementById(idname));
}
which is pretty much the same as getting the return value from the callback, and return it. Here's a verbose version:
function getIdElements(idname, callback) {
var element = document.getElementById(idname);
var callbackRetrunValue = callback(element);
return callbackRetrunValue;
}
In your code: with no return value, the value you read from your getIdElements is simply undefined: What does javascript function return in the absence of a return statement?
callback returns. You simply ignore callback's return value.getIdElements shouldn't both close with the value I've returned inside?foo and bar. You know what they are doing but you don't know if they return a value. Now you have a function function baz() { foo(); bar(); }. According to your logic, if foo returned a value, baz would return that value too and bar would not even be executed. That's quite unintuitive. It would mean you'd always have to know how a function is implemented, which completely defeats creating a function for abstraction in the first place.