the rest operator javascript
function sum(...numbers) {
return numbers.reduce((accumulator, current) => {
return accumulator += current;
});
};
sum(1,2) // 3
sum(1,2,3,4,5) // 15the rest operator javascript
function sum(...numbers) {
return numbers.reduce((accumulator, current) => {
return accumulator += current;
});
};
sum(1,2) // 3
sum(1,2,3,4,5) // 15rest parameters
// Before rest parameters, "arguments" could be converted to a normal array using:
function f(a, b) {
let normalArray = Array.prototype.slice.call(arguments)
// -- or --
let normalArray = [].slice.call(arguments)
// -- or --
let normalArray = Array.from(arguments)
let first = normalArray.shift() // OK, gives the first argument
let first = arguments.shift() // ERROR (arguments is not a normal array)
}
// Now, you can easily gain access to a normal array using a rest parameter
function f(...args) {
let normalArray = args
let first = normalArray.shift() // OK, gives the first argument
}how to assign an rest operator in javascript
function multiply(multiplier, ...theArgs) {
return theArgs.map(element => {
return multiplier * element
})
}
let arr = multiply(2, 1, 2, 3)
console.log(arr) // [2, 4, 6]js spread parameters
// seperate each element of array using ...
let list = ['a','b','c'];
let copy = [...list, 'd', 'e']; // ['a', 'b', 'c', 'd', 'e']
//use for infinite parameters to a function
function toDoList(...todos) {
//todos is an array, so it has map function
document.write(
`<ul>${todos.map((todo) => `<li>${todo}</li>`).join("")}</ul>`
);
}
toDoList("wake up", "eat breakfast", ...list); //ul containing: wake up eat breakfast a b crest parameter
deleteUser = (id: number): void => {
const { [id]: user, ...updatedUsers } = this.users;
this.users = updatedUsers;
};
//a function within a class to delete a use. Also uses TS assignments on line 1.
//On line 2, [id]: user, uses both a computed property and the rest parameter to remove the user by id from this.users. this.users is then reassigned to updatedUsers, which we accessed via the spread operator.Copyright © 2021 Codeinu
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