How do I impliment a Charge Jump?

Hi there, I'm trying to make a game similar to Jump King where that game allows the player to hold down the jump button for a few seconds and when released, the power of the jump increases for however long the button was held (although there is a cap for how long this charge can be stored for).

I am having trouble trying to figure out how to impliment this feature into my game.

Create a variable jumpStr

> Keyboard is Space down 
... Set jumpStr to clamp(jumpStr+dt*500, 100, 1000)


Keyboard On Space released
... Player set jump strength to jumpStr
... Player Simulate Jump
... Set jumpStr to 0

This will allow charge the jump from 100 to 1000 over ~2 seconds.

Thank You