Need Help Understanding this Javascript Algorithm

I’m trying to learn Javascript but I am stuck on this problem. I keep going around in circles and have been staring at this problem for hours. I can’t seem to find a solution that I can wrap my head around… :frowning: Any help will be appreciated. I don’t understand how to get the output, there’s so much going on. It’s fun but I’m having a hard time lol

It would be easier for us if you could copy and paste your code into your original post instead of showing a screenshot. You can edit your original post and delete the image. Also, what exactly are you expecting this code to do? For example, can you show us what you want to display as an output to the console?


To enter a code block into the forum, precede it with a line of three backticks and follow it with a line of three backticks to make easier to read. See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.


What exactly are you trying to do? Predict the output of that piece of code? Go line by line and expression by expression. Write down a timeline of the values of your variables.

line 1: msg = 'helloworld' – assigns ‘helloworld’ to msg, msg is a string of length 10.

line 3: first for loop
initialisation: var x=-2 – defines x and sets its value to -2
test: x<msg.length-1 – test if x (-2) is smaller than msg.length-1 (9). It’s true so we enter the loop and execute the block

line 5: if (msg.length==5)false: msg.length is 10, not 5, so we skip the if block lines 6 to 11 and we enter the else block on line 12

line 15: enter a second for loop
initialisation: var i=msg.lengthi is defined and set to 10
test: i>(msg.length-1) – is i (10) > msg.length-1 (9)? true so we execute the for block

line 17: console.log(i) – write 10 to the console

for block for loop 2 is finished, we execute the incrementation part of the loop: i--i is now 9

Then it’s the test again i>(msg.length-1) – is i (9) > msg.length-1 (9)? It’s false so we exit loop 2.

There’s no more code in the for block for loop 1, so we execute the incrementation part of the loop: x++ – x is now -1

Back to the test for loop 1: x (-1) < 9? true so we execute the for block again

The if condition will never evaluate to true since msg is not changed anywhere so we execute the else statement again. Since all the code there depends on msg.length, the result is the same: it outputs 10 to the console.

And it keeps doing that for every value of x between -2 and 8 inclusive. It exits for loop 1 when x has been set to 9.

So what this piece of code does is output the number 10 eleven times. Unless I got something wrong somewhere.