Can I draw a weapon between attacks?

Question

Suppose a 5th level fighter with Extra Attack, armed with a greatsword and a javelin.

Extra Attack:

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

Suppose the following sequence of events:

1. The fighter starts their turn already wielding their greatsword.
2. The fighter uses their full movement speed to get to melee range of an enemy.
3. The fighter uses their attack action to strike an enemy: The enemy is killed on the first strike.
4. The nearest remaining enemy is 15 feet away.

So at this point, can the fighter draw their javelin as their free object interaction for the turn, then throw it at the nearby enemy as their extra attack?

I think this is okay: You can move between attacks, and moving feels like it should be a bigger deal mechanics-wise than a free object interaction.

Moving Between Attacks:

If you take an action that includes more than one weapon attack, you can break up your movement even further by moving between those attacks. For example, a fighter who can make two attacks with the Extra Attack feature and who has a speed of 25 feet could move 10 feet, make an attack, move 15 feet, and then attack again.

The dodgy bit might be letting go of the greatsword with the main hand to draw and throw the javelin. But I think Jeremy Crawford coveres that on Twitter:

Jeremy Crawford:
A two-handed weapon needs two hands to be used, but not necessarily two to be carried.

This related comment for reaction spells sort of applies here too:

Simon Orion:
Would this cover Reaction Spells

Jeremy Crawford:
Yes

So it sounds like going from holding a weapon with two hands to holding it with one hand is a non-action.

So I think this checks out.

Just setting up a character that I want to focus on two handed weapons. I would like the ability to attack at range in the same round if I can get it.

Answer 1

You can draw a weapon between attacks

Other Activity on Your Turn states:

You can also interact with one object or feature of the environment for free, during either your move or your action. For example, you could open a door during your move as you stride toward a foe, or you could draw your weapon as part of the same action you use to attack.

This means that you do not need to break up an action to interact with an object, because that interaction is part of the action and it occurs during the action. The attack (or attacks, if you have a feature like Extra Attack) also occur as part of the Attack action, so it stands to reason that you can perform the interaction in no particular order, including between attacks as well.

Of course, drawing a weapon is an interaction that requires a free hand, but as you've already pointed out a two-handed weapon only requires both hands when you attack with it, not during the whole Attack action. The Weapon Properties state as much:

Two-Handed. This weapon requires two hands when you attack with it.

Therefore, you can do the following during one Attack action:

• make an attack with a two-handed weapon (such as a greatsword)
• draw another weapon (such as a javelin)
• make an attack with the other weapon (if, like the javelin, it is not two-handed)