[Javascript Crocks] Safely Access Object Properties with `prop`

In this lesson, we’ll use a Maybe to safely operate on properties of an object that could be undefined. We’ll use our initial code as the basis for a prop utility function that can be reused with different objects and various property names. Instead of just blindly asking for a property, this version of prop will drop us into the safe confines of a Maybe, giving us a Just when the property exists and a Nothing for an undefined property. Once we’ve built up our own prop utility, we’ll refactor the code one more time to take advantage of the built-in proputility provided by the crocks library.

 

When you want to pull out a value from object or array, you might doing like this:

const safe = require('crocks/Maybe/safe');
const { inc } = require('./utils');
const { not, compose, isNil, prop } = require('ramda');

// check the value is not undefined or null
const isNotNil = safe(compose(not, isNil));
// check object's prop value is not undefined or null
const safeProp = propName => obj => isNotNil(prop(propName, obj));
// get 'page' prop from the object as Maybe type
const safePage = safeProp('page');
// data
const qs = { page: 4, pageSize: 10, totalPages: 203 };
//default value is 1
const result = safePage(qs).option(1);

console.log(result); // 4

 

Actually from the code above we write many code, we use Ramda lib for utils functions and  safe prop method.

const { not, compose, isNil, prop } = require('ramda');

const isNotNil = safe(compose(not, isNil));
const safeProp = propName => obj => isNotNil(prop(propName, obj));

 

 

Actually crocks lib provide 'prop' method to simply the code:

const prop = require('crocks/Maybe/prop');
const { inc } = require('./utils');

const safePage = prop('page');

const qs = { page: 4, pageSize: 10, totalPages: 203 };
const result = safePage(qs).option(1);

console.log(result);