I have an inherited class, and need the parent to have a virtual method, which is overridden in the child class. This method is called from the base constructor, and needs access to instance properties, so it needs to be a lambda function, so "this" is "_this". The problem is, overriding a lambda method does not work for me like overriding a non-lambda does. Is this possible? If not, I'd like to understand why.
Also, will "this" always be the same as "_this" when the method is only called from the constructor?
class Base {
protected prop = null;
constructor() {
this.init();
this.initLambda();
}
init() {
console.log("Base init");
}
initLambda = () => {
console.log("Base initLambda");
}
}
class Derived extends Base {
constructor() {
super();
}
init() {
console.log("Derived init");
}
initLambda = () => {
//let x = this.prop;
console.log("Derived initLambda");
}
}
Output:
Derived init
Base initLambda
Well, you can't have that.
There's an issue that was opened but it was closed as "by design".
You should use regular methods:
class Base {
protected prop = null;
constructor() {
this.init();
this.initLambda();
}
init() {
console.log("Base init");
}
initLambda() {
console.log("Base initLambda");
}
}
class Derived extends Base {
constructor() {
super();
}
init() {
console.log("Derived init");
}
initLambda() {
console.log("Derived initLambda");
}
}
And then it will work.
As for keeping the right this
, you can always pass a call to the method as an arrow function:
doit() {
setTimeout(() => this.init(), 1);
}
Or use the Function.prototype.bind function:
setTimeout(this.init.bind(this));
Also, the _this
thing that the typescript compiler produces is just a hack to polyfil the arrow functions for ES5, but if you change the target to ES6 then it won't use it.
You can save the bound methods as members:
class Base {
...
public boundInit: () => void;
constructor() {
...
this.boundInit = this.initLambda.bind(this);
setTimeout(this.boundInit, 500);
}
...
With that, when I do new Derived()
this is what I get:
Derived init
Derived initLambda // after 200 millis
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With