IntersectionObserver: "Uncaught TypeError: Cannot read property of undefined" when called onIntersection()

Question

I have following code:

var ObjectOne = {
    a : {
        b : 4,
        ...
    }        
    observer : 0,
    ...

    init() { 
        this.a.b = 5;           
        ...
        this.observer = new IntersectionObserver(this.onIntersection, ...);               
        this.observer.observe(...);
        ...       
    }
    onIntersection(entries, observer) {
        ...
        var test = this.a.b;
        ...
    }
}

And when run it, i have an error at a moment, when onIntersection() is executed. The error is: Uncaught TypeError: Cannot read property 'b' of undefined. How i can pass 'this' instance of ObjectOne to onIntersection() function?

Answer 1

Thanks to Heretic Monkey for useful link How to access the correct this inside a callback? - it was helpful and give me a direction for search. And more helpful information was at Use of the JavaScript 'bind' method. Adding bind() function solve the problem:

var ObjectOne = {
    a : {
        b : 4,
        ...
    }        
    observer : 0,
    ...

    init() { 
        this.a.b = 5;           
        ...
        this.observer = new IntersectionObserver(this.onIntersection.bind(this), ...);               
        this.observer.observe(...);
        ...       
    }
    onIntersection(entries, observer) {
        ...
        var test = this.a.b;
        ...
    }
}