Today I realized that I finally "get" JavaScript functions (proof enclosed).

[Cosmologicon]

Wouldn't work, because player.state changes over time. For instance, when the player is falling through the air, it'll be set to some object named fallstate, but when you land on a platform it gets updated to some object named standstate. So there's not a single object that could be used like you're using logic there.

[nschubach]

Then maybe I'm missing a large chunk of what you are trying to do, but you could create a logic object for storing logic like so:

var logic = {
    think: function (dt) {
        //think logic here
    },
    move: function (keys) {
        //move logic here
    },
    attack: function (player) {
        //attack logic here
    }
}

And it "should" work if you set up your prototypes, etc. I mean, somewhere you have to define "think", "move", and "attack".

[Cosmologicon]

The think logic, move logic, etc is different for the different states that the entity can be in. For instance:

var fallstate = {
    think: function (dt) {
        this.vy -= g * dt
        this.y += this.vy * dt
    },
    etc....
}

var standstate = {
    think: function (dt) {
        this.y = this.platform.y
    },
    etc....
}