How to use the pegjs/lib/compiler/opcodes.APPEND function in pegjs

"        case " + op.POP_CURR_POS + ":", // POP_CURR_POS
      "          peg$currPos = stack.pop();",
      "          ip++;",
      "          break;",
      "",
      "        case " + op.POP_N + ":", // POP_N n
      "          stack.length -= bc[ip + 1];",
      "          ip += 2;",
      "          break;",
      "",
      "        case " + op.NIP + ":", // NIP
      "          stack.splice(-2, 1);",
      "          ip++;",
      "          break;",
      "",
      "        case " + op.APPEND + ":", // APPEND
      "          stack[stack.length - 2].push(stack.pop());",
      "          ip++;",
      "          break;",
      "",
      "        case " + op.WRAP + ":", // WRAP n
      "          stack.push(stack.splice(stack.length - bc[ip + 1], bc[ip + 1]));",
      "          ip += 2;",
      "          break;",
      "",
      "        case " + op.TEXT + ":", // TEXT
      "          stack.push(input.substring(stack.pop(), peg$currPos));",
      "          ip++;",
      "          break;",
      "",
      "        case " + op.IF + ":", // IF t, f
      indent10(generateCondition("stack[stack.length - 1]", 0)),

ip++;
            break;

          case op.POP_N: // POP_N n
            stack.pop(bc[ip + 1]);
            ip += 2;
            break;

          case op.NIP: // NIP
            value = stack.pop();
            stack.pop();
            parts.push(stack.push(value));
            ip++;
            break;

          case op.APPEND: // APPEND
            value = stack.pop();
            parts.push(stack.top() + ".push(" + value + ");");
            ip++;
            break;

          case op.WRAP: // WRAP n
            parts.push(
              stack.push("[" + stack.pop(bc[ip + 1]).join(", ") + "]")
            );
            ip += 2;
            break;

          case op.TEXT: // TEXT
            parts.push(
              stack.push("input.substring(" + stack.pop() + ", peg$currPos)")
            );

function buildAppendLoop(expressionCode) {
    return buildLoop(
      [op.WHILE_NOT_ERROR],
      buildSequence([op.APPEND], expressionCode)
    );
  }