arrowFunction.js

class TestClass {

    constructor() {
        a = 0;
    }

    increment() {
        this.a++;
    }

    strangeLoop() {
        // This will fail
        [1].forEach(function() {
            this.a = 1;
        })
    }

    fixedStrangeLoop() {
        var self = this;
        [1].forEach(function() {
            self.a = 2;
        })
    }

    arrowLoop() {
        [1].forEach(() => {
            this.a = 3;
        })
    }
}

var x = new TestClass();

x.strangeLoop();
x.fixedStrangeLoop();
x.arrowLoop();