how to combine multiple arrays into one javascript variable code example

Example 1: concatenate multiple arrays javascript

const array1 = ['a', 'b', 'c'];
const array2 = ['d', 'e', 'f'];
const array3 = [...array1, ...array2];

console.log(array3);
// expected output: Array ["a", "b", "c", "d", "e", "f"]

Example 2: javascript merge multidimensional array

const _questions = _.map(this.sections, section => section.questions);
const questions  = Array.prototype.concat.apply([], _questions);