CODE EXAMPLE FOR JAVASCRIPT

function for flatten an array

const arr = [1, 2, [3, 4, [5, 6]]];

// to enable deep level flatten use recursion with reduce and concat
function flatDeep(arr, d = 1) {
   return d > 0 ? arr.reduce((acc, val) => acc.concat(Array.isArray(val) ? flatDeep(val, d - 1) : val), [])
                : arr.slice();
};

flatDeep(arr, Infinity);
// [1, 2, 3, 4, 5, 6]



// Faltten an array
const age=[1,2,
           [12,23,[75,34,[2,34]],[32,45]],
           [3,456],
           [56,5]]
// to store resultant array
let result=[]
function flattenArray(inputArray)
{
  inputArray.map((value)=>{
    if(Array.isArray(value))
    { 
      flattenArray(value)
    }
    else{
      result.push(value)
    }})
  }
// calling function to fallten an array
flattenArray(age);