Yuto

Explains how to get value by key, get key by value, and use an enum as an object key. Some functions don't behave as expected when an enum has number values or mixed type data. All enum-related solutions are on this page.

The spread operator (three dots) is used to copy an array and expand an array to pass the values to another object or function parameters. It can also be used as rest parameters in a function to indicate that the function can take as many arguments as you want. The spread operator is handled as a shallow copy. Therefore you need to be careful if you use it for an object that has objects in the property list.

try-catch doesn't catch an error thrown in timer friend functions setTimeout, setInterval and setImmediate.Using timer f...

Recursive setTimeout and setInterval behave differently. You need to know the difference and which to use depending on the specification. This post explains how to implement it and the difference with images.

Inner class or nested class can be defined if you assign a class with an equal operator. Another way is to define a function that returns an object. If you call the function somewhere, the object can be handled as a class.