problem appending data from an array to html code example

Example 1: javascript append array to end of array

const new_array = old_array.concat([value1[, value2[, ...[, valueN]]]])

Example 2: add item to array javascript

const arr1 = [1,2,3]
const newValue = 4
const newData = [...arr1, obj] // [1,2,3,4]