Call `echo` in a custom function should not echo "Pending..."

[pearmini]

//➜ Pending…
function raster(callback, [width, height]) {
  let output = "";
  for (let i = 0; i < height; i++) {
    const x = i / height - 1;
    for (let j = 0; j < width; j++) {
      const y = j / width - 1;
      output += callback(x, y);
    }
  }
  echo(output);
}