Recursion~ Popular concepts ~

Recursion is probably one of the oldest concepts in programming. It's the paradigm where a function calls itself. We usually use this technique to solve problems that require breaking them into smaller subproblems.

In JavaScript, my favorite use case is reading a deeply nested object field. Let's say that we have the following:

const user = {
  profile: {
    age: 36,
    name: { first: "Krasimir", last: "Tsonev" },
  },
};

We want to read the last name of the user. We have to write user.profile.name.last. And of course, if some of the data is missing, we will get:

Cannot read properties of undefined (reading 'last')

We use helpers like lodash's get method to solve this problem.

get(user, 'profile.name.last', 'unknown');

This utility safely tries to read the value and returns the "unknown" string if it doesn't exist.

Here is how the implementation of such utility may look like:

function get(obj, path, fallback) {
  const parts = path.split(".");
  const key = parts.shift();
  if (typeof obj[key] !== "undefined") {
    return parts.length > 0 ?
      get(obj[key], parts.join("."), fallback) :
      obj[key];
  }
  return fallback;
}

console.log(get(user, "profile.name.first")); // Krasimir
console.log(get(user, "profile.age")); // 36
console.log(get(user, "profile.registered")); // undefined
console.log(get(user, "profile.registered", false)); // false

Notice how get calls itself again until it reaches the last part of the path.