Mastering JavaScript Functional Programming - Second Edition

Working with prisms

Working with prisms is similar to using lenses, except for what happens when an attribute is not present. Let's take a look at an example from the previous section:

const author = {  user: "fkereki",  name: {    first: "Federico",    middle: "",    last: "Kereki"  },  books: [    { name: "GWT", year: 2010 },    { name: "FP", year: 2017 },    { name: "CB", year: 2018 }  ]};

If we wanted to access the user attribute using prisms, we would write something like the following—don't worry about the details; we'll look at the actual implementation later:

const pUser = prismProp("user");console.log(review(pUser, author).toString()); /*    fkereki*/

Here, we define a prism using a prismProp() function, which parallels our previous lensProp() one. Then, ...