However, Steve Bruce is yet to make up his mind as to which will take the reigns between the sticks with a decision due to be made as pre-season begins.
Button played the last five games of the EFL Championship campaign as the Baggies’ season drew to an anticlimactic close.
But Bruce must consider both of his options as he plans for another busy schedule in the second tier.
Signed from Brighton and Hove Albion in 2020, the shot-stopper provides a breadth of Championship experience with over 150 appearances at this level.
Now 33 years old, he's certainly the most experienced option for the Albion boss despite playing second fiddle for larger parts of his career.
The past five matches of their campaign have meant Button has had the chance to prove himself ahead of the other options.
With Johnstone on his way out of the exit door, Bruce confirmed following the 3-1 defeat to Stoke City that he wouldn't play any further part in the season.
And Button stepped into his shoes for the home straight, keeping three clean sheets in as many games at the tail end of the campaign.
Since coming into the side, the 33-year-old has proved to have a good range of passing throughout a variety of different angles.
This was exemplified by his assist during the final game of the season - a home victory over already-relegated Barnsley.
Having done little wrong during his spell in the net at the end of the season and after signing a two-year contract extension last week, you feel that Button is likely to start the race for number one in pole position.
With only two Championship games under his belt to date, the 25-year-old comes in as the more inexperienced at this level.
Having not made the matchday squad for 35 of Albion's 46 games this season, after signing a new four-year deal, his thoughts will be turned to that number one spot.
A product of the Baggies' academy, the 'keeper has been with the club since the age of thirteen and has been more than patient in waiting for his chance.
But he had to wait eleven years after joining them to make his first-team debut, which came in a 6-0 Carabao Cup defeat to Arsenal where former boss Valerien Ismael opted for a very young side to prevent injuries to first-choice players.
His only taste of second-tier action came at Luton Town where he spent two games on an emergency loan.
Winning promotion to the third tier with the latter, his performances brought plenty of admirers with Luton looking to sign him permanently back in the summer.
After signing his new long term contract it seems as if Bruce has seen those qualities and hopes to include him in those first-team plans in 2022/23.
It would be unfair not to mention Albion's brightest young prospect in the goalkeeping department.
Josh Griffiths has had two loan spells, like Palmer in both League One and Two, firstly with Cheltenham Town where he helped secure the league title and most recently (like Palmer again) with Lincoln.
West Brom feel they have a future number one with Griffiths and are believed to be considering another loan move for the 20-year-old next season.