In a medium-sized bowl, whisk together the pineapple juice, soy sauce, brown sugar, ketchup, ginger, and garlic until fully combined.
Arrange the chicken thighs in the crockpot and pour the prepared sauce mixture over the top. Set the crockpot to cook on low for 5 to 7 hours, allowing the chicken to become tender and infused with the sauce.
Once the cooking time has passed, remove the chicken from the crockpot. Whisk in the cornstarch to thicken the sauce to your desired consistency.
At this stage, you can choose to serve the chicken in its whole thigh pieces, accompanied by the sauce. Alternatively, shred the chicken and return it to the crockpot, stirring it into the sauce. Shredded chicken is perfect for serving as a filling for sandwiches or a topping for rice.