Javascript - filter, includes, forEach

1. filter - return Array

FYI. map - also return Array

const numbs = [10, 20, 30];

const callBack = (n) => n > 15;
const biggerThan15 = numbs.filter(callBack);
console.log(biggerThan15); //[ 20, 30 ]

2. forEach - doesn’t return array

The forEach() method executes a provided function once for each array element.

let maybeJs = "Javascript";
let js = ["js", "jscript"];
if (!js.includes(maybeJs.toLowerCase())) {
  js.push(maybeJs.toLowerCase());
}
console.log(js); //[ 'js', 'jscript', 'javascript' ]

3. filter - return boolean

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

let maybeJs = "Javascript";
let js = ["js", "jscript"];
if (!js.includes(maybeJs.toLowerCase())) {
  js.push(maybeJs.toLowerCase());
}

console.log(js);