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ecmascript-6arrow-functions

es6katas.org Kata #6: arrow functions - binding

I am learning ECMAScript6 in es6katas.org, which is great and highly recommended. I am currently stuck at this pretty basic kata about arrow function. I can't seem to understand what the author meant in the second test:

class LexicallyBound {

    getFunction() {
        return () => {
              return new LexicallyBound();
        }
    }

    getArgumentsFunction() {
        return function() {return arguments}
    }

}

it('bound at definition time, use `=>` ', function() {
    var bound = new LexicallyBound();
    var fn = bound.getFunction();

    assert.strictEqual(fn(), bound);
});

Can someone assist in figuring it out?

Solution

  • I think it wanted you to change getFunction to return this.

    Reason: Fat arrow function's this is bounded to the defining context (the bound object) when it was defined - when bound was created - instead of having a dynamic this like normal functions.