Collatz chain

Goal: follow the 3n+1 chain from a starting number down to 1, counting the moves and writing down every number you visit.

The rule

Start with any positive whole number. Make a move:

if the current number is even, halve it
if it is odd, triple it and add 1

Keep making moves until you reach 1. (Nobody has ever found a starting number that doesn't get there, but nobody has proved it either.)

Worked example

Starting at 6:

Move	Current number	Even or odd?	Next number
1	6	even	3
2	3	odd	10
3	10	even	5
4	5	odd	16
5	16	even	8
6	8	even	4
7	4	even	2
8	2	even	1

So steps is 8 and path is "6 -> 3 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1": every number visited, starting number and final 1 included, with -> between them.

If start is 1, you're already there: steps is 0 and path is "1".

Rules

Keep the line let start = ...; at the top of the file. The tests replace the number on it. It is always a positive whole number.
Declare const steps (a number) and const path (a string).
Follow the chain with a while loop.
Some chains climb a long way before they fall. 27 takes 111 moves and goes above 9000, and starting numbers near a million must still finish quickly.
Don't use var, and don't use loose == or !=.
To look at your boxes while you work, add console.log(steps, path); at the bottom and run node collatz_chain.js.

What you'll practice

A while loop that runs until a condition says stop
Choosing a track with if and else on every lap
Keeping several let boxes in step with each other
Building text with a template literal, one piece per lap
Copying results into const boxes once the work is done

Run it

gonomicon fetch fs-week-2/01-07-collatz-chain
cd 01-07-collatz-chain
gonomicon test
gonomicon submit

Hints

You don't know how many moves it will take, only when to stop: when the number reaches 1. That's a job for while. Keep the number you're working on in its own let box, so start stays as it was.
Before the loop, make three let boxes: the current number, a move counter at 0, and a text box that begins with the starting number. Each lap: decide even or odd with % 2, change the current number, add 1 to the counter, and add -> plus the new number to the text.
while (current !== 1) { if (current % 2 === 0) { current = current / 2; } else { current = current * 3 + 1; } count++; trail += -> ${current}; }. After the loop, put the results into the boxes the tests look at: const steps = count; and const path = trail;.