Can you use a bonus action before a held readied action?

Question

I know you can not "Ready" a bonus action. But can you ready an attack action and use the bonus action before the attack action when the action is triggered?

The rule for bonus actions says:

You choose when to take a bonus action during your turn, unless the bonus action's timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action.

An example of bonus action's timing specified is like with Monk's Flurry of Blows:

Immediately after you take the Attack action on your turn, you can spend 1 ki point to make two unarmed strikes as a bonus action.

So unless the bonus action specifies that you have to take it at a specific time, you can take the bonus action at any point in your turn.

If a member of your party is talking to a guard 40 feet away, could you, for example, do the following?

1. Ready an action, the trigger being "If the guard draws his weapon I am going to attack"
2. The guard draws his weapon triggering your readied action.
3. Use your bonus action to cast 'Misty Step,' which has no timing restrictions, to move 30' towards them, use 10 feet of movement, and attack.

Answer 1

Your reaction happens immediately in response to the trigger.

The rules for Ready state:

When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger.

The rules for Reactions state:

A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

You must use your reaction immediately in response to the trigger, so you cannot cast a bonus action spell between the trigger and your reaction.

You can only take a bonus action on your turn.

Notably, you can only take a bonus action on your turn:

You choose when to take a bonus action during your turn

So for this situation to even come up, the enemy would have to draw their sword on your turn, which would be quite unusual, but is possible. You cannot move or take a bonus action between the trigger and the reaction, but the following situation could happen:

• Guard's Turn: Uses Ready action to draw sword if you move.
• Your turn: Use Ready action to attack if Guard draws sword, you move. Your move triggers the guard's readied action, and they draw their sword. Them drawing their sword is the trigger for you readied action, so you must choose to take it or to ignore the trigger. You cannot cast misty step until after you take your readied action or choose to ignore the trigger.

It would be quite odd for this to happen, but it's technically possible. But again, you still cannot cast misty step between the trigger and the reaction.

Answer 2

No. Bonus actions are for your turn.

Let's look at the terms

Bonus Actions: Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.[emphasis mine]

Reactions: Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's.

Ready: Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn... [Further in this section]... When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell's magic requires concentration (explained in chapter 10).

Nowhere is there a loophole that lets you add a bonus action to your reaction. In fact, it specifically says you cannot cast a bonus action spell as a readied action.