append.js

export default function append<T>(arr: T[], val: T): T[] {
  return [...arr, val];
}

tryAppend.js

import {sampleOne, types} from 'babel-plugin-transform-flow-to-gen/api';
import append from './append.js';

const strArgsGen = append.asGenerator(types.string());

const strArgs = sampleOne(strArgsGen);

console.log(strArgs);
// [ [ '1dv', '', 'b' ], '4w0' ]

const numArgsGen = append.asGenerator(types.number());

const numArgs = sampleOne(numArgsGen);

console.log(numArgs);
// [ [ 0, -1 ], 2 ]