javascript - Apply a filter inside a 'for...in' statement

Question

How can I apply a filter inside a 'for...in' statement?

In other words, I want to iterate only some of the keys of an object.

It's pretty easy with a for...of statement, for example:

for (const key of Object.keys(obj).filter(key => key.startsWith("0x"))) {
    ...
}

But I want to use for (const key in obj) instead.

How can I apply a filter inside that statement?

Answer 1

Simply append an if statement after your for(...) expression:

for (const key in obj) if (key.startsWith("0x")) {
   ...
}