The rest parameter syntax allows a function to accept an indefinite number of arguments as an array, providing a way to represent variadic functions in JavaScript.

The JavaScript exception "rest parameter may not have a default" occurs when a rest parameter has a default value. Because the rest parameter always creates an array, the default value would never apply.

The for await...of statement creates a loop iterating over async iterable objects as well as sync iterables. This statement can only be used in contexts where await can be used, which includes inside an async function body and in a module.

A marker trait which represents “panic safe” types in Rust.

The propertyIsEnumerable() method of Object instances returns a boolean indicating whether the specified property is this object's enumerable own property.

Property accessors provide access to an object's properties by using the dot notation or the bracket notation.

The findIndex() method of TypedArray instances returns the index of the first element in a typed array that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned. This method has the same algorithm as Array.prototype.findIndex().

A modifier overrides flag settings in a specific part of a regular expression. It can be used to enable or disable flags that change the meanings of certain regex syntax elements. These flags are i, m, and s.

The JavaScript exception "can't access lexical declaration 'X' before initialization" occurs when a lexical variable was accessed before it was initialized. This happens within any scope (global, module, function, or block) when let or const variables are accessed before the place where they are declared is executed.

The concat() method of Array instances is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.