why use assign and timing of invoke

[shmdhussain]

Hi David,

This week I watched the xstate course on frontendMasters.

I have few doubts.

--first one is:

Why we need to use assign when we can directly do the same thing in action function.

I heard you are explaining this , but I am unable to understand the mutable and immutable context. could you point me to some pointers or explain me

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--Second One is:

When will the invoke triggered, after entering into the state?

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thanks in advance,

[Andarist]

Why we need to use assign when we can directly do the same thing in action function.

You can't. assign is used to manipulate machine's context value which is treated as immutable for a variety of reasons. While you probably can get away with:

function someAction(ctx) {
  ctx.foo.bar = 'newValue'
}

you won't be able to manipulate the context correctly for any top-level key, so this won't work as expected:

function someAction(ctx) {
  ctx.foo = 'newValue'
}

Either way - we do not recommend direct mutations to manipulate the context value because it makes certain things impossible (like going back in history in the visualizer etc).

When will the invoke triggered, after entering into the state?

Yes, always after entering the state.