In this section, you're going to learn the ins and outs of the arrow function. It's an ES6 feature, and we have taken a little look at it. Inside notes.js we used it in a few basic examples to create methods such as fetchNotes and saveNotes, and we also passed it into a few array methods like filter, and for each array, we used it as the callback function that gets called once for every item in the array.

Now if you try to swap out all of the functions in a program with arrow functions, it's most likely not going to work as expected because there are some differences between the two, and it's really important to know what those differences are, so you can make the decision to use a regular ES5 function or an ES6 arrow function.