Angular what's the meaning of these three dots in @NGRX
The three dots are known as the spread operator from Typescript (also from ES7).
The spread operator return all elements of an array. Like you would write each element separately:
let myArr = [1, 2, 3];return [1, 2, 3];//is the same as:return [...myArr];This is mostly just syntactic sugar as it compiles this:
func(...args);to this:
func.apply(null, args);In your case this gets compiled to this:
return [...state, action.payload];//gets compiled to this:return state.concat([action.payload]);
It is a spread operator (...) which is used for spreading the element of an array/object or for initializing an array or object from another array or object.
Let's create new array from existing array to understand this.
let Array1 = [ 1, 2, 3]; //1,2,3
let Array2 = [ 4, 5, 6]; //4,5,6
//Create new array from existing array
let copyArray = [...Array1]; //1,2,3
//Create array by merging two arrays
let mergedArray = [...Array1, ...Array2]; //1,2,3,4,5,6
//Create new array from existing array + more elements
let newArray = [...Array1, 7, 8]; //1,2,3,7,8