reference an item in a map kjs code example

Example 1: initialize a map js

let map = new Map()
map['bla'] = 'blaa'
map['bla2'] = 'blaaa2'

console.log(map)  // Map { bla: 'blaa', bla2: 'blaaa2' }

Example 2: array mdn map

let new_array = arr.map(function callback( currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])