Passing an array as the code to eval in setTimeout?

Question

Today my friends sent my some code that did something unexpected:

setTimeout(["console.log(1", "2)"], 1000)

I expected this to fail or do some magic, but it just prints 1 2 after 1 second. I can see it possibly evaluating the array to "console.log(1,2)" using a simple array.join(','), but why does that happen?

I've looked into the eval capabilities of setTimeout, but it should only do a function or a string. The use of an array here doesn't make any sense, and searching Google for why this does work turns up nothing, or even close use cases.

Answer 1

setTimeout can evaluate a string as javascript, if the value is not a function it will then convert the value to a string, probably by using toString()

You can see if you do this

"" + ["console.log(1", "2)"]

or

["console.log(1", "2)"].toString();

you get

'console.log(1,2)'

Then it get's evaluated accordingly

Answer 2

If it is not a function then it uses .toString() to get a string value.