An approach to problem-solving

I've been considering an approach to problem solving and code writing, and it's, solve in parts until you solve in full. Let me explain.

I'm currently working on a feature for code-migration-helpers and I'm stuck. I think I understand how it should work, but representing it in code seems challenging because there are several moving parts. Basically, I want to add a tool for adding/modifying index files in folders, and propagating added/modified index files to parent folders. Seems simple, but when you consider questions like,

• what if the file or symbol is already imported?
• what if it's imported but not exported?
• should we use wildcard * exports, and how should we handle existing wildcard exports? The list goes on...

A way to approach this complexity in code is to solve partially, like divide-and-conquer. To solve this problem, I need 3 things:

• what symbols to export,
• what symbols have been exported, and
• exporting new symbols.

Having separated the concerns, I have 3 placeholder functions:

async function decideSymbolsToExport(filepath: string, opts: Opts): Promise<string[]> {}
async function filterExistingExportedSymbols(symbols: string[], opts: Opts): Promise<string[]> {}
async function exportSymbols(symbols: string[], filepath: string, opts: Opts): Promise<string[]> {}

Now, what it'll eventually be may be a bit more complex than this, but I can pick each part and solve it as if the rest is in place.

I'm pretty sure there's most probably a name for this technique, but let me know what you think, and possible improvements.