Javascript for loop, counter inside?

Question

I'm a beginner learning loops.

I made a for loop like this:

for (i = 0; i < 5; i++) {
    console.log("Counting...");
}

As expected I get the output "Counting..." five times.

I modified the loop and put the counter inside it instead (maybe you shouldn't do this, I'm just trying things out).

for (i = 0; i < 5;) {
    console.log("Counting...");
    i++
}

Now i get:

Counting...
Counting...
Counting...
Counting...
Counting...
4

Where is this 4 coming from? What does it mean?

There is no 4 that gets printed: fiddle. You must have another console.log somewhere after. — sp00m
– sp00m, Commented Jun 3, 2014 at 7:59
You should have got "Counting..." five times followed by an undefined in the first case? — Bergi
– Bergi, Commented Jun 3, 2014 at 8:01

kamituel · Accepted Answer · 2014-06-03 08:05:13Z

2

You probably are runnig this in Developer Tools or similar. "4" isn't actually printed, it's the return value of the last statement from the for loop.

When you ran your first loop, you probably saw this:

Counting...
Counting...
Counting...
Counting...
Counting...
undefined

(undefined is a return value in first case, because console.log() does not return anything). In second case, undefined is being replaced by 4.

edited Jun 3, 2014 at 8:05

answered Jun 3, 2014 at 7:59

kamituel

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2 Comments

Johan Dahl Over a year ago

Thank's, this clears it up. I didn't see any 'undefined' being printed out on Codeacademy where I'm doing this, maybe they strip it out. When I put my first loop in my own console, I did get undefined.

kamituel Over a year ago

This is added as a convienience in development. To quickly evaluate some expression, you only have to type "2 + 5" and not "console.log(2 + 5);"

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