原数组的值全部复制给新数组，在进行各项操作之后不会对原素组产生影响，原数组不变

function sort(arr, fn) {

var newArr = [];

for (var i = o; i < arr.length; i ++) {

newArr[newArr.length] = arr[i];

}

for (var i = 0; i < newArr.length - 1; i ++) {

var flag = true;

for (var j = 0; j < newArr.length - 1 - i; j ++){

if (fn(newArr[j] > newArr[j + 1]) > 0){

var temp = newArr[j];

newArr[j] = newArr[j+1];

newArr[j+1] = temp;

flag = false;

}

}

if (flag) {

break;

}

}

return newArr;

}

var array = [3, 2, 1];

console.log(arr);

console.log(sort(array, function (a, b){

return a - b;

}));

console.log(arr);