Question

Hey I was wondering if you can help me out with these two questions:

1. Correct the implementation of JavaScript function below assuming that the documentation is correct. Use a highlighter to identify your corrections.
/** Maps items from an array using a function.
* @arg {array} array Array to map.
* @arg {function(item,index)} fun Function to call for each item. The return value is appended to the output array, unless undefined.
* @arg {array} [out] Optional output array.
* @ret {array} The output array. */
function map(array, fun, out) {
var n = array.length,
m = out.length,
i;
if (out === null)
out = []
for (i = 0; i <= n; ++i)
v = array[i];
v = fun(v, i);
if (v !== undefined) {
out[++m] = v;
}
}

2. Assuming the implementation in question 1 is correct and it functions as documented, what is the return value of the following?
var a1 = [2, 4, 5];
var a2 = ["hello"];
function incr(v, i) {
if (v % 2) return v + 1;
}
return map(a1, incr, a2);

Answer 1

1.

function map(array, fun, out) {
var n = array.length,
m = out.length,
if (out === null)
out = []
for (let i = 0; i <= n; ++i)
v = array[i];
v = fun(v, i);
if (v !== undefined) {
out[m++] = v;
}

return out;
}

2.

incr(2, 0) -> undefined since 2 % 2 != 1

incr(4, 0) -> undefined since 4 % 2 != 1

incr(5, 0) -> 6 since 5 % 2 = 1

Hence, 5 is appended to the array a2.

Hence, the contents of ar are:

["hello", 5]