What does Three points … in Javascript? known as the Spread or Rest Operator

About

The … three points may refer to:

• the spread operator. It 'expands' an array into its elements,
• or the rest parameter. It 'condenses' multiple elements into a single element

Usage example

Object Merge

You use it for object merge

obj1 = { color: "blue" };
obj2 = { color: "red", length: 10 };
obj3 = { name: "TheName" };
console.log('With Spread');
console.log({...obj1, ...obj2, ...obj3});

• Result: Note that the values in conflict are overwritten and not added. The last object to the right has precedence.

Syntax

Spread

The spread syntax ¹⁾ allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) or multiple variables (for destructuring assignment) are expected.

Spread syntax can be applied only to iterable objects

• For function calls:

myFunction(...iterableObj);

• For array literals:

[...iterableObj, 4, 5, 6];

Rest

The rest parameter ²⁾ syntax allows to represent an indefinite number of arguments as an array.

• For function definition:

function f(a, b, ...theArgs) {
  // ...
}

where:

• …theArgs is an array

Documentation / Reference