js: accessing scope of parent class
Use an Arrow Function
An arrow function does not have it's own
this
. Thethis
value of the enclosing lexical scope is used; arrow functions follow the normal variable lookup rules. So while searching forthis
which is not present in current scope they end up findingthis
from its enclosing scope.
Normal function syntax
function(param1, param2) {}
Arrow function syntax
(param1, param2) => {}
Usage
const simpleClass = function () {
this.status = "pending";
this.target = jqueryObject;
this.updateStatus = function() {
this.target.fadeOut("fast", () => { // notice the syntax here
this.status = "complete"; // no change required here
});
};
};
Using an Arrow function within a ECMAScript 2015 Class
class simpleClass {
constructor() {
this.status = 'pending';
this.target = jqueryObject;
}
updateStatus() {
this.target.faceOut('fast', () => {
this.status = "complete";
});
}
}
const s = new simpleClass();
s.updateStatus();
Described code works only in modern browsers.
I will post this answer to this old question anyway as no one yet posted this before.
You can use the bind
method on your function calls to define the scope which this
belongs to.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind
Normaly everytime you create a method - this
belongs to the current scope of the function. Variables from scope2 can't see variables from scope1.
e.g.
function(){
// scope 1
this.baz = 'foo';
function(){
// scope 2
this.baz // not defined
};
};
with the bind
method you can define the scope from this
inside the function. So using .bind(this)
you're telling the called function that their own scope from this
is referred to the scope of the parent function, like:
function(){
// scope 1
this.baz = 'foo';
function(){
// scope 1
this.baz // foo
}.bind(this);
};
so in your case, this would be an example using the bind
method
var simpleClass = function () {
this.status = "pending";
this.target = jqueryObject;
this.updateStatus = function() {
this.target.fadeOut("fast",function () {
this.status = "complete"; //this needs to update the parent class
}.bind(this));
}.bind(this);
};
By setting "this" to a variable you can access easily. Like:
$("#ImageFile").change(function (e) {
var image, file;
var Parent=this;
if ((file = Parent.files[0])) {
var sFileExtension = file.name.split('.')[file.name.split('.').length - 1];
if (sFileExtension === "jpg" || sFileExtension === "jpeg" || sFileExtension === "bmp" || sFileExtension === "png" || sFileExtension === "gif") {
var reader = new FileReader();
reader.onload = function (e) {
alert(Parent.files[0].name);
};
reader.readAsDataURL(Parent.files[0]);
}
else { alert('Wrong file selected. Only jpg, jpeg, bmp, png and gif files are allowed.'); }
}
})
You set "this" to a variable in the parent function and then use it in the inner function.
var simpleClass = function () {
this.status = "pending";
this.target = jqueryObject;
var parent = this;
this.updateStatus = function() {
this.jqueryObject.fadeOut("fast",function () {
parent.status = "complete"; //this needs to update the parent class
});
};
};