This a typescript file that explains the difference between an arrow function and a named function in Javascript runtime

ArrowVsNamedFunctions.ts

const l = console.log

class Asdf {
    memberProp = 3450

    methodA = () => {
        const a = this.memberProp
        return a
    }

    methodB() {
        const a = this.memberProp
        return a
    }

    constructor() {
        const objWithArrow = {
            meth: this.methodA
        }
        const objWithFunction = {
            meth: this.methodB
        }

        const objWithArrowResult = objWithArrow.meth()
        l(objWithArrowResult) // Prints 3450

        const objWithFunctionResult = objWithFunction.meth()
        l(objWithFunctionResult) // Prints `undefined` because this is not *lexical*.
                                // Once a named (or anonymous) function is assigned to a property of
                                // an object, its `this` is exchanged for that assignee.
                                // Arrow functions, however, maintain their `this` value.

        /*
            Could've declared as

            const objWithFunction = {
                meth: this.methodB,
                memberProp: 3450
            }
        */
    }
}