DENVER — Those who know him best. Those who are in the clubhouse and on the field with Jacob deGrom have the strongest feelings about the subject.

Don’t even think about trading deGrom and, while you are at it, Mets, lock him up contractually for a long as you possibly can.

No-nonsense pitching coach Dave Eiland listed all the off-the-charts attributes deGrom brings, and then told The Post this when asked if deGrom should be traded for prospects:

“Absolutely not. It’s crazy, it’s asinine, these guys don’t just fall off trees, it’s total nonsense,’’ Eiland said before the Mets played the Rockies on Tuesday night at Coors Field, one night after deGrom pitched eight spectacular innings in a 12-2 win over Colorado.

“Say you got five prospects, who is to say those prospects are going to work out?’’ Eiland said. “Who’s going to fill Jake’s innings not only this year, but in 2019 and 2020? He is the pitcher every team is looking for. Hey, I’m just a pitching coach, not a manager or a GM, but I’ve been in this game for over 30 years, you don’t trade a guy like that, because you can’t replace him.’’

Veteran third baseman Todd Frazier said deGrom is “the most dominant pitcher in the major leagues. He works fast, mows guys down, he takes the pressure off us. I was talking to [Rockies third baseman Nolan] Arenado [Monday] and he said, ‘I’m scuffling but I was feeling a little better until I had to come in today to face deGrom. Worst nightmare.’

“I would never want to trade a person like that, a guy that dominant,’’ Frazier added.

He smiled and said, “unless you are going to get two Mike Trouts.’’

Not one, two.

Center fielder Michael Conforto concurred, saying, “You absolutely do not trade him. As a teammate, he doesn’t necessarily have to say much but you can tell he is the leader of the pitching staff. What he does on the field and off the field, that’s what you want in your ace. I came up in 2015 and saw him step into that role and seen him grow and grow, I would never want to see him go.’’

Noted Eiland, “When he is in a big moment out there he always seems to come through. He’s had the bases loaded four times with no outs and has got out of it all four times. He just takes it to another level in big moments and that’s what a true No. 1 does.

“Not to get too corny, but he is a special guy, a special pitcher,’’ Eiland added. “Those don’t come around all the time. This team, this organization, this fan base is very fortunate to have a guy like that. Some teams go years and years and years and sometimes decades without having a guy like that at the top of your rotation. He’s accountable, he doesn’t make excuses, he doesn’t point the finger at anybody. He brings his game to another level to pick up people around him and he’s one of the Mets’ own.”

DeGrom turned 30 Tuesday. He is under control for two more years. Mets ownership would be wise to extend deGrom for three years after that. His ERA is 1.51, the lowest in the majors and lowest in team history after 15 starts.

Dwight Gooden had a 1.66 ERA in 1985 after 15 starts. DeGrom is tied for fifth in the majors in strikeouts (120) and third with a .535 OPS allowed.

Mickey Callaway was pitching coach for the Indians when they extended a 28-year-old Corey Kluber for five years, $38.5 million. He knows the value of a Cy Young pitcher. “Having a Jacob deGrom on your staff is essential to you winning ever,’’ Callaway said. “Why trade him? He would be so hard to replace. You could get five really, really good players and you still wouldn’t be able to replace what Jacob deGrom does every day. He is irreplaceable.’’

There is only one Jacob deGrom.

The Mets are lucky to have him. Those in the clubhouse and on the field know that best of all. Keeping deGrom should be the Mets’ top priority.