Spencer was born and raised in Long Island, New York[2][3] and attended Bay Shore High School where she played soccer and ran track.[4] Spencer was twice-named the high school team's most valuable player and served as captain.[4] She led the team in scoring and assists for four seasons and set a school record for career goals.[4] She played club soccer for the Albertson Fury 90 and won three consecutive state championships with the team.[4]
In 2013, Spencer signed with the Washington Spirit for the inaugural season of the NWSL.[8][9] She made 17 appearances for the club.[10] The team finished in last place during the regular season with a 3–14–5 record.[11]
Spencer joined the Western New York Flash ahead of the 2014 NWSL season.[14] She made 22 appearances for the club, starting in 9 matches and scoring 3 goals.[10] She scored her first goal for the Flash during a 2–1 over FC Kansas City on May 8.[15] The Flash finished in seventh place with a 8–12–4 record.[16]
Returning to the Flash for the 2015 season, Spencer started in 19 of the team's 20 matches.[10] She scored a game-winning goal against the Washington Spirit, resulting in a 3–2 win.[17] The Flash finished in seventh place with a 6–9–5 record.[18]
Sydney FC, 2014–16
In September 2014, Spencer signed with Sydney FC of the Australian W-League for the 2014 season.[19] She was a starting forward in all 13 games that she played and scored 8 goals.[10] During her debut for the team during a match against Adelaide United, Spencer scored the game-winning brace resulting in a 2–0 win.[20] Sydney finished in fourth place during the regular season with a 5–3–4 record and secured a berth to the Final Stages.[21] The team was defeated by Perth Glory in the semi-finals.[22] Spencer was named Players' Player of the Year by her teammates.[23]
Returning to Sydney for the 2015–16 season, Spencer was a starting player in all 14 games in which she played and scored 4 goals during the regular season, primarily playing as a midfielder.[10] Sydney finished in third place with a 6–5–1 record and advanced to the semi-finals where they faced Canberra United.[24][25] During the match, Spencer scored the game-winning goal in the 67th minute to lead Sydney to a 1–0 win and berth to the 2016 W-League Grand Final.[26]
Orlando Pride, 2016–17
In November 2015, Orlando Pride selected Spencer as their fourth pick in the 2015 NWSL Expansion Draft.[27] During the team's inaugural season, Spencer was a starting forward in 17 of the 20 games she played.[10] She scored her first goal for the Pride — a game-winner — during a 1–0 win over the Houston Dash on June 24.[28] The goal was named Goal of the Week for Week 10 of the 2016 season.[29] Two days later, she scored the team's lone goal during a 2–1 loss against Portland Thorns FC.[30] The Pride finished their inaugural season in ninth place with a 6–13–1 record.[31] Spencer scored four goals during the regular season.[10]
Canberra United, 2016–17
Spencer joined Canberra United on loan for the 2016–17 W-League season.[32][33] She was a starting player in 8 of her 10 appearances for the club, helping Canberra finish in first place during the regular season with a 7–3–2 record and advance to the semi-finals.[34]
OL Reign, 2018–2020
In January 2018, Spencer was traded to OL Reign (then known as Seattle Reign FC).[35] She made her debut for the club during the team's home opener win against the Washington Spirit. The game marked Spencer's 100th cap in the NWSL.[36] Spencer tore her ACL in the first game of the 2019 season and missed the remainder of the season.[37][10]
Melbourne City FC, 2018–19
Spencer joined Melbourne City on loan for the 2018–19 W-League season. She made her debut in City's season opener, a 2–0 loss to Canberra United but scored a hat-trick the following weekend in the team's home opener, a 3–1 victory over Sydney.[38]
Houston Dash, 2021
Spencer made her debut for Houston Dash in a 1-0 win against the Kansas City Current on June 6, 2021.[10] She made 18 appearances for the club during the 2021 season notching 874 minutes on the pitch. She scored the game-winning goal against her former club Reign FC on July 2 in a 2-0 win.[39] The Dash finished the regular season in seventh place with a 9–10–5 record.[40]
Angel City FC, 2022–24
On December 16, 2021 Spencer was selected in the fifth round of the 2022 NWSL Expansion Draft by expansion club Angel City FC and signed a two-year contract.[41] On September 11, 2022, Spencer made her 150th NWSL appearance against her former club team, the Houston Dash. Spencer recorded 876 minutes and 17 clearances during the 2022 season and she started 10 of 15 regular season matches during their inaugural season which saw them finish in eighth place with a record of 8–9–5.[42]
During the 2023 season, Spencer scored her first goal for the club, a match winner in a 1–0 victory against Kansas City Current which helped Angel City along its path to its first ever NWSL Playoff appearance where they finished the season fifth overall with a 8–7–7 record.[43][44]
Spencer made her first start of the 2024 season on April 13, 2024 against Chicago Red Stars, playing a key role in Angel City's first win and clean sheet of the season. The game also marked her 175th NWSL regular-season appearance.[45] Spencer made her 50th appearance for Angel City on September 1, 2024, in a home match against the Chicago Red Stars which finished as a 2–1 victory. Spencer is the first outfield player to reach this milestone for Angel City, and second overall after goalkeeper DiDi Haračić.[46] After the concluson of the 2024 season Spencer became a free agent and on December 10, 2024, Angel City announced they would not be signing Spencer to a new contact.[47] Spencer finished her time at Angel City as the player with the most appearances across all competions with 76.
Other work
Spencer created lifestyle brand "Jas It Up Headbands" in 2016. In 2019, while recovering from an ACL injury she rebranded it to "Jas It Up".[48] The sustainable lifestyle brand sells clothing and accessories. The mission of the brand "is to educate and inspire people to lead an eco-conscious and socially aware lifestyle in an effort to uplift our communities, empower our youth, and protect our future on this planet."[49]