You can add a basic condition that checks if your player is currently moving on the y axis, like:

if (player.velocity.y == 0) player.velocity.y = -10;

You can extend this further by adding a falling state, as to say, if by the odd chance your character's y velocity is 0 when they've reached the peak of the jump, you don't want to be able to reset the player's y velocity back to -10 (this would cause more jump spam).

So what you could do is within your event listener:

if (player.velocity.y !== 0 && !player.travelingUpwards) {
  player.velocity.y = -10
  player.travelingUpwards = true
}

Then for every frame within your animation loop, check if the player is falling down:

if (player.velocity.y > 0) {
  player.travelingUpwards = false
}

Combined together, you should prevent jump spam and prevent a player from jumping if they reach the peak and their y velocity is 0.

Ive tried adding the code into my event listener and going through the steps of adding the code for the traveling upwards but the code displays an error im assuming that im placing the code in the wrong place?