传递数组不起作用使我在控制台中未定义

Question

In below javascript code, if I only prints nums which is array pass to the function. it prints the array as well as gives undefined. So below logic gives an answer but in next line it prints out undefined.

function getSecondLargest(nums) {

       let deceding = nums.sort(function(a, b){return b-a});


    for(let i = 0; i<deceding.length ; i++)
        {
            if(deceding[i]>deceding[i+1])
                {
                    console.log(deceding[i+1]);
                    break;
                }
        }


}

Answer 1

Pretend deceding is [0, 1, 2] .

You have i < deceding.length , so i will range between 0 and 2 (Less than length, which is 3).

Next you do console.log(deceding[i + 1]); , but for the later iterations of the loop i + 1 will be greater than 2 which is the last index of the array, meaning it is undefined. ie, you try to get deceding[3] which is undefined.

Answer 2

Can you change an execute environment? I've never seen undefined in my node.

Answer 3

I guest that you run this function on chrome console . Actually your function is return nothing. So it is console undefined . Is this the same what you got ? http://prntscr.com/hgma9g

The chrome console alway print out what returned from last line of code. So if this is an assignment or function call without return a value it will print undefined . So don't worry, your function worked as expected.

There is a way to by pass this by assign and return the value you want to log in the function. :)