src/language-js/print/assignment.js/printAssignment
function printAssignment(
  leftNode,
  printedLeft,
  operator,
  rightNode,
  printedRight,
  options
) {
  if (!rightNode) {
    return printedLeft;
  }

  const printed = printAssignmentRight(
    leftNode,
    rightNode,
    printedRight,
    options
  );

  return group(concat([printedLeft, operator, printed]));
}