What does ellipses do in JavaScript?

In Javascript, ellipses ( … ) are used for two separate shorthands — rest syntax and spread syntax . Rest syntax will set the remaining elements of a collection to a defined variable.

(three dots in JavaScript) is called the Spread Syntax or Spread Operator . This allows an iterable such as an array expression or string to be expanded or an object expression to be expanded wherever placed. This is not specific to React. It is a JavaScript operator.31 May 2017

Rest operator . When used within the signature of a function, where the function’s arguments should be, either replacing the arguments completely or alongside the function’s arguments, the three dots are also called the rest operator.

The spread operator is a new addition to the set of operators in JavaScript ES6 . It takes in an iterable (e.g an array) and expands it into individual elements. The spread operator is commonly used to make shallow copies of JS objects. Using this operator makes the code concise and enhances its readability.

The && is the exact same operator as you would find in any javascript expression , such as… if( condition1 && condition2) { } It is a feature of javascript that an expression of the form… (condition1 && condition2) will evaluate to condition2, if condition1 is true, or null if condition1 is false.