Objects

In javascript, object by default are copied as a reference, i.e. only the memory address is copied. To use deep copy, one can use loadash _.cloneDeep().

The Garbage collector

It basically perform a dfs on the reachability graph, marking all possibe nodes reachable from the main node and deletes all the unmarked nodes.

This basic algorithm is done with some optimzations.

this keyword

this takes the shape of the context, in case of non-strict mode the browser’s window.

new keyword

Execute the function with prepended this = {} and postpended return this.

new.target keyword

This is a special keyword, which contains the reference to the function called with new operator i.e. the body of the function. By default, it is undefined.

Returns null

// the given function returns `null` if not found
let html = document.querySelector('.elem').innerHTML; // error if it's null

Optional chaining ?.

The object returns undefined if object?. is used and object is either undefined or null.

Symbols

https://javascript.info/symbol

Primitive methods & object wrappers

Primitive data types do not have methods as per say, but when one calls the methods, there exist an object wrapper which is created for example String for str and provides the methods to mutate the underlying primitive data type.

https://javascript.info/primitives-methods