创建一个函数，返回一个包含5到118之间所有奇数的数组

Question

Here's my code, but it's not working. Is my thought-process correct? Please help:

function sum_odd(arr) {
   arr = [];
   for (var i = 5; i < 119; i++) {
       if (i % 2 === 1) {
           arr.push(i);
       }
   }
   return arr; 
}

Answer 1

Calling sum_odd() returns: [5, 7, 9, 11, 13,..., 117]

Your code works fine but you don't need the arr argument which in fact is not used.

 function sum_odd(){ var arr = []; for (var i = 5; i < 119; i++) { if (i % 2 === 1) { arr.push(i); } } return arr; } var x = sum_odd(); document.write(x); 

It is a better idea to save half of the loop iterations and do no checks on i by incrementing i by two.

If you want to modify the argument, remove the var arr = [] statement.

 function sum_odd(arr) { for (var i = 5; i < 119; i += 2) { arr.push(i); } return arr; } var res = []; sum_odd(res) document.write(res); 

Answer 2

I think the issue you have is not with the actual code, but the way arguments are passed. When you call arr=[] , it does not mutate, or change, the original array to be an empty array.

What it does is it redirects the reference that the function holds--the variable arr once held a reference to the parameter passed, but after you assign it to [] , it is no longer pointing to the parameter, but it is instead pointing to a new array somewhere else that's initialized to be empty.

So if you run the code

array = [];
sum_odd(array);

Then the sum_odd function does not modify the array passed; instead, it creates a new array and returns it, and in this case the return value isn't used, so array remains empty.