On page 30, "In addition, you can use the const keyword to lock the value referenced by a variable, as well processing collections of objects with the Array methods map, reduce, filter, and others in a very idiomatic way."

That's not accurate. Const prevents redeclaring a variable, but it does not lock down values. For instance:

const foo = 'bar';
foo = 'bar2'; //error

but...
const foo = ['bar', 'bar2'];
foo[0] = 'bar3'; // ['bar3', 'bar2']

I know what you mean, but it may be confusing to others.