Unexpected result when checking undefined value

Question

I have an array of objects with a length of at most 4 and at least 1. Here, I check which elements exist and do things accordingly.

function sendToGroup(receiver_group) {
  if (receiver_group[0] !== undefined){
    console.log(receiver_group[0])
  }

  if(receiver_group[1] !== undefined){
    console.log(receiver_group[1])
  }

  if(receiver_group[2] !== undefined){
    console.log(receiver_group[2])
  }

  if(receiver_group[3] !== undefined){
    console.log(receiver_group[3])
  }
}

When I give the array of 2 elements to this function, I see first and second element as expected in the console output but I also see an undefined in the line of

console.log(receiver_group[2])

How is this even possible? If it is undefined(which it is) this logging code should not get executed.

Edit: Chrome says the length of the array is 2. Which It is. receiver_group is an array. which has the content of

[{id:12, name:"name", age:"21"}, {id:22, name:"name", age:25}]

Also same thing doesn't happen for the item 4 which has the index of 3.

Are you sure you don't have a `console.log` after printing `undefined`? How do you know it's from `console.log(receiver_group[2])`? — Carcigenicate, Mar 02 '19 at 20:24
chrome shows the logging is coming from which line. That is how I know the code gets executed. Also following functions are works too. — Akil Demir, Mar 02 '19 at 20:27
Also, why not simply `receiver_group.forEach(x => console.log(x));`? — John Coleman, Mar 02 '19 at 20:29
@JohnColeman I know that is the way to do it. But that is not the problem here. — Akil Demir, Mar 02 '19 at 20:30
@AkilDemir I meant what's the value of it. Please put that into your post — Aniket G, Mar 02 '19 at 20:32
Perhaps it is the *string* `"undefined"`? On the one hand `undefined !== undefined` is always false, but on the other hand, `"undefined" !== undefined` is true. What does `console.log(receiver_group.length);` return in this case? — John Coleman, Mar 02 '19 at 20:32
Try running `undefined == undefined` in the JavaScript console and see if the answer is what you expected. My guess is that you're looking for the `typeof` function. — mzedeler, Mar 02 '19 at 20:38
When I take your current code and add to it the line `sendToGroup([{id:12, name:"name", age:"21"}, {id:22, name:"name", age:25}]);` in a .js file and run it in node, I see nothing unexpected printed . Are you sure that you are not running that line in the console? Please give a [mcve] -- with an emphasis on *verifiable*. ` — John Coleman, Mar 02 '19 at 21:16

score 4 · Answer 1 · answered Mar 02 '19 at 20:48

4

It is also printing undefined, if I execute the below code:

if(1==2){}

In the console you can type a name of a variable (for example try typing window) and it prints info about it. When you run any void function (like console.log) from the console, it also prints out info about the return value, undefined in this case.

So, the undefined printed after logging [0] and [1] value is the correct behavior as it is trying to print the return value which is undefined.

Please refer to the answer: Chrome/Firefox console.log always appends a line saying undefined

answered Mar 02 '19 at 20:48

Srijan

257
1
8

My point was It should not even enter the inside of if statement. Because What I am saying is log the output if it is not undefined in the code. – Akil Demir Mar 02 '19 at 20:55
1

@AkilDemir The point of this answer is that perhaps it isn't entering that statement at all -- the `undefined` could be triggered by the *second* log -- if you are running this code directly in the console rather than from a .js file. As an experiment, replace `console.log(receiver_group[2])` by `console.log("test")`. Is `"test"` printed? – John Coleman Mar 02 '19 at 20:57
I am running the code from .js file and not only logging, the code under the console.log is also running. I mean tries to run but since receiver_group[2] is undefined It can't and gives error. – Akil Demir Mar 02 '19 at 21:04

Unexpected result when checking undefined value

1 Answers1