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.
The exercise doesn't pass checking. What to do? 😶
If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:
- Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨
Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.
My code is different from the teacher's one 🤔
It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.
In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.
I've read the lessons but nothing is clear 🙄
It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.
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