function map(arr, fn){
let newArr = [];
for ( let i = 0; i < arr.length; i++ ){
newArr[i] = fn(arr[i], i, arr)
}
return newArr;
}
function filter(arr, fn){
let newArr = [];
for ( let i = 0; i < arr.length; i++ ){
if ( fn(arr[i], i, arr)){
newArr.push(arr[i]);
}
}
return newArr;
}
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