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

1
      )),
      "",
      "        case " + op.MATCH_STRING_IC + ":", // MATCH_STRING_IC s, a, f, ...
      indent10(generateCondition(
        "input.substr(peg$currPos, (peg$consts[bc[ip + 1]] as string).length).toLowerCase() === peg$consts[bc[ip + 1]]",
        1
      )),
      "",
      "        case " + op.MATCH_REGEXP + ":", // MATCH_REGEXP r, a, f, ...
      indent10(generateCondition(
        "(peg$consts[bc[ip + 1]] as RegExp).test(input.charAt(peg$currPos))",
        1
      )),
      "",
      "        case " + op.ACCEPT_N + ":", // ACCEPT_N n
      "          stack.push(input.substr(peg$currPos, bc[ip + 1]));",
      "          peg$currPos += bc[ip + 1];",
      "          ip += 2;",
      "          break;",
      "",
      "        case " + op.ACCEPT_STRING + ":", // ACCEPT_STRING s
      "          stack.push(peg$consts[bc[ip + 1]]);",
      "          peg$currPos += (peg$consts[bc[ip + 1]] as string).length;",
      "          ip += 2;",
      "          break;",
      "",
      "        case " + op.FAIL + ":", // FAIL e
      "          stack.push(peg$FAILED);",
      "          if (peg$silentFails === 0) {",
      "            peg$fail(peg$consts[bc[ip + 1]] as ILiteralExpectation);",
      "          }",

"input.substr(peg$currPos, " +
              eval(ast.consts[bc[ip + 1]]).length +
              ").toLowerCase() === " +
              c(bc[ip + 1]),
              1
            );
            break;

          case op.MATCH_REGEXP: // MATCH_REGEXP r, a, f, ...
            compileCondition(
              c(bc[ip + 1]) + ".test(input.charAt(peg$currPos))",
              1
            );
            break;

          case op.ACCEPT_N: // ACCEPT_N n
            parts.push(stack.push(
              bc[ip + 1] > 1 ?
              "input.substr(peg$currPos, " + bc[ip + 1] + ")" :
              "input.charAt(peg$currPos)"
            ));
            parts.push(
              bc[ip + 1] > 1 ?
              "peg$currPos += " + bc[ip + 1] + ";" :
              "peg$currPos++;"
            );
            ip += 2;
            break;

          case op.ACCEPT_STRING: // ACCEPT_STRING s
            parts.push(stack.push(c(bc[ip + 1])));
            parts.push(

let expectedIndex = addConst(
          "peg$literalExpectation("
            + "\"" + js.stringEscape(node.value) + "\", "
            + node.ignoreCase
            + ")"
        );

        // For case-sensitive strings the value must match the beginning of the
        // remaining input exactly. As a result, we can use |ACCEPT_STRING| and
        // save one |substr| call that would be needed if we used |ACCEPT_N|.
        return buildCondition(
          node.ignoreCase
            ? [op.MATCH_STRING_IC, stringIndex]
            : [op.MATCH_STRING, stringIndex],
          node.ignoreCase
            ? [op.ACCEPT_N, node.value.length]
            : [op.ACCEPT_STRING, stringIndex],
          [op.FAIL, expectedIndex]
        );
      } else {
        let stringIndex = addConst("\"\"");

        return [op.PUSH, stringIndex];
      }
    },