I recently tried to assist a colleague with an issue in JavaScript involving an undefined variable within a Vue.js app.

Now I have encountered this issue several times and never really gotten to the crux of the matter other than I know it’s because the context of this changes, depending on where you are in your code.

It was during this tongue twisting exercise that he found a useful document that gives an outline more elegantly than I could phrase.


Since arrow functions provide a lexical this value, the this inside our function() refers to the window instead of our Vue object which breaks our current implementation! When attempting to get this.item, we will actually be looking at window.item which is currently undefined.