There are differences between arrow functions and traditional functions, as well as some limitations:
JavaScript Advance
In JavaScript, standard built-in object-copy operations (spread syntax, Array.prototype.concat(), Array.prototype.slice(), Array.from(), Object.assign(), and Object.create()) do not create deep copies (instead, they create shallow copies).
A deep copy of an object is a copy whose properties do not share the same references (point to the same underlying values) as those of the source object from which the copy was made.
A shallow copy of an object is a copy whose properties share the same references (point to the same underlying values) as those of the source object from which the copy was made.
As a result, when you change either the source or the copy, you may also cause the other object to change too — and so, you may end up unintentionally causing changes to the source or copy that you don't expect.
That behavior contrasts with the behavior of a deep copy, in which the source and copy are completely independent.
Currying is an advanced technique of working with functions. It’s used not only in JavaScript, but in other languages as well.
Currying is a transformation of functions that translates a function from callable as f(a, b, c) into callable as f(a)(b)(c).
Currying doesn’t call a function. It just transforms it.
Let’s see an example first, to better understand what we’re talking about, and then practical applications.
JavaScript Hoisting refers to the process whereby the interpreter appears to move the declaration of functions, variables or classes to the top of their scope, prior to execution of the code.
Hoisting allows functions to be safely used in code before they are declared.
Variable and class declarations are also hoisted, so they too can be referenced before they are declared. Note that doing so can lead to unexpected errors, and is not generally recommended.
The nullish coalescing operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.
The optional chaining operator (?.) enables you to read the value of a property located deep within a chain of connected objects without having to check that each reference in the chain is valid.
The ?. operator is like the . chaining operator, except that instead of causing an error if a reference is nullish (null or undefined), the expression short-circuits with a return value of undefined. When used with function calls, it returns undefined if the given function does not exist.
for...in
Show demo below
const arr = ['a', 'b', 'c'];
for (index in arr) { console.log(index); }
//ouput:
//1
//2
//3