typescript external callback binding within classes

user_7446971 0
Viewed 42

I'm trying to bind properties of a class to a callback inside that class.

Quick example:

// caller
const first = (): void => {
  const testClass = new TestClass();
  testClass.second(() => {
    console.log(this.member) // error TS2532: Object is possibly 'undefined'
  }
}

// TestClass
...
member: string = 'test';

second(cb: () => void) {
 const self = this;
 cb.bind(self)();
}

this seems to be possibly undefined.

How can I access the classes members from an outside callback?

typescript callback binding javascript
2 Answers

The Arrow Functions are for automatic binding to the current scope and parent objects, so you can't call them with bindings of your callbacks. so here javascript interpreter is trying to find the parent which the callback has been defined before.

// caller
const first = (): void => {
  const testClass = new TestClass();
  testClass.second(function() {
    console.log(this.member)
  }
}
user_54054150

Add a condition before the console log to avoid print undefined objects.

from your example:

// caller
const first = (): void => {
  const testClass = new TestClass();
  testClass.second(() => {
    if (this.member) console.log(this.member)
  }
}

// TestClass
...
member: string = 'test';

second(cb: () => void) {
   const self = this;
    cb.bind(self)();
}
user_96687920
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