index.js

const { join } = require('path');
const { readFileSync, mkdirSync, writeFileSync } = require('fs');
const core = require('@actions/core');
const artifact = require('@actions/artifact');
const rimraf = require('rimraf');

const WORKDIR = join(process.cwd(), '_persist_action_dir');

async function storeData(variable, data){
    var client = artifact.create();
    const file = join(WORKDIR, `${variable}.txt`);

    // cleanup old directories if needed
    rimraf.sync(WORKDIR);
    mkdirSync(WORKDIR);
    
    writeFileSync(file, data, { encoding: 'utf8' });
    await client.uploadArtifact(variable, [file], process.cwd())
}
async function loadData(variables){
    var client = artifact.create();
    
    // cleanup old directories if needed
    rimraf.sync(WORKDIR);
    mkdirSync(WORKDIR);

    for (const v of variables) {
        let data;

        try {
            const file = join(WORKDIR, `${v}.txt`);
            await client.downloadArtifact(v);
            data = readFileSync(file, { encoding: 'utf8' }).toString();
        } catch (error) {
            core.warning(`Variable ${v} not found`)
        }
        core.setOutput(v, data);
        core.exportVariable(v, data);
        // store the same data with a fixed prefix so it can be iterated over if needed
        core.exportVariable(`persist-action-data-${v}`, data);
    }
}

async function runAction(){
    const inputs = {
        data: core.getInput('data'),
        variable: core.getInput('variable'),
        retrieve: core.getInput('retrieve_variables'),
    }

    if (inputs.retrieve) {
        const vars = inputs.retrieve.split(',').map(v=>v.trim());
        await loadData(vars)
        return;
    }

    await storeData(inputs.variable, inputs.data)
}

runAction().then(() => {
    core.info('Action completed successfully');
  })
  .catch(e => {
    core.setFailed(e.toString());
  });