JavaScript: Chaining method calls

Numbers have a method that converts them to a string:

const peopleCount = 5;
peopleCount.toString(); // '5'

Will the following code work, and if so, what will it print?

const name = 'Tirion';
console.log(name.length.toString());

It's the first time we've seen several consecutive periods, but all of the above operations here are familiar. Everything happening in this code is a mix of language features we already know. This happens quite often in programming. Even if you don't know the syntax, you can try combining different approaches, and there's a good chance it'll work.

The easiest way to understand how this code works is to break the chain into separate operations:

const name = 'Tirion';
const len = name.length;
console.log(len.toString());

These examples all do the same thing. We can perform operations sequentially, creating constants in between, or build a continuous chain of properties and methods. Computations in chains always go from left to right.

One more example:

const name = 'Tirion';
console.log(name.toUpperCase().toLowerCase());

You'll need a bit of mental effort for this code. It's important to understand that .toLowerCase() is applied to the result of the .toUpperCase() function. And toUpperCase() returns a string. Rookies often make mistakes with chains of methods; they forget to call them:

const name = 'Tirion';
// This code will work incorrectly.
console.log(name.toUpperCase.toLowerCase());

Following this idea, it's possible to build infinitely long (though, in this case, useless) chains:

// What is the result of this call?
console.log(name.toUpperCase().toLowerCase().length.toString().length);

_This trick won't work with functions because they are usually nested, f(f(f())), which complicates analysis. Yet this doesn't mean that you can't do it nicely - you can and should. Other languages implement it by composing functions or using a pipeline operator, which, incidentally, is starting to be used more and more in JavaScript: https://github.com/tc39/proposal-pipeline-operator.

Instructions

Using the slice() method, get part of the sentence assigned to the constant text, starting from the 5th character and ending on the 15th character. Process the resulting substring using the .trim() method and print the length of the final substring. Run these methods in a chain without any intermediate variables.

• slice()
• trim()