The in operator returns true if the specified property is in the specified object or its prototype chain.

Method definition is a shorter syntax for defining a function property in an object initializer. It can also be used in classes.

The Set object lets you store unique values of any type, whether primitive values or object references.

Symbol is a built-in object whose constructor returns a symbol primitive — also called a Symbol value or just a Symbol — that's guaranteed to be unique. Symbols are often used to add unique property keys to an object that won't collide with keys any other code might add to the object, and which are hidden from any mechanisms other code will typically use to access the object. That enables a form of weak encapsulation, or a weak form of information hiding.

The bitwise OR (|) operator returns a number or BigInt whose binary representation has a 1 in each bit position for which the corresponding bits of either or both operands are 1.

The logical OR (||) (logical disjunction) operator for a set of operands is true if and only if one or more of its operands is true. It is typically used with boolean (logical) values. When it is, it returns a Boolean value. However, the || operator actually returns the value of one of the specified operands, so if this operator is used with non-Boolean values, it will return a non-Boolean value.

The function declaration creates a binding of a new function to a given name.

The height attribute defines the vertical length of an element in the user coordinate system.

The Object.defineProperty() static method defines a new property directly on an object, or modifies an existing property on an object, and returns the object.

The push() method of Array instances adds the specified elements to the end of an array and returns the new length of the array.