Write some code, that will flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].

flat.js

// version 1 
const flat = (array) => {
  let list=[]
   array.map((item) => { 
      if(Array.isArray(item)){
         list=[...list,...flat(item)]
      }else{ 
        list.push(item)
      }
    })
   
   return list
}
// version 2
const flatten = (array) =>{
    return array.reduce((prev,current)=>{
       return Array.isArray(current) ? prev.concat(flatten(current)) : prev.concat(current)
    },[])
}
let original1 = [[1,2,[3]],[[[[4]],[6]],[[7]]],8] 
let original2 =[[1,2,[3]],4]
console.assert( JSON.stringify([ 1, 2, 3, 4, 6, 7, 8 ]) === JSON.stringify(flatten(original1)), 
{"message":"sorry: flatten fail the test"} )
console.assert( JSON.stringify([ 1, 2, 3, 4]) === JSON.stringify(flatten(original2)), 
{"message":"sorry: flatten fail the test"} )