Calling push() on array, TypeError: Attempted to assign to readonly property - reactjs

Question

Working in React Native. I'm trying to declare an array and then push things to said array, but I'm getting the error TypeError: Attempted to assign to readonly property
CONTEXT:
The app prints via a thermal printer.
The print method receives an array of commands
Example:
print([{appendText: "blah"}, {
appendCutPaper: StarPRNT.CutPaperAction.PartialCutWithFeed,
}]
The print method is asynchronous and if you attempt to call the method again before the last call has finished, it errors.
Because of #2, we created a queue system that accepts a job (array of commands) and then works through the jobs synchronously.
In a React component, I'm attempting to create a job by declaring an empty array named printJob
and then pushing various commands to it. In this case, we take a snapshot of a View and then push the commands returned by the printImage method to the printJob array.
onClick={() => {
const printJob = []
viewShot.current
.capture()
.then((uri) => {
printJob.push(...printImage(uri))
})
.catch((err) => alert(err))
newPrintJob(printJob)
}
printImage returns the array of commands to print an image and cut the paper:
const CUT_PAPER = {
appendCutPaper: StarPRNT.CutPaperAction.PartialCutWithFeed,
}
export function printImage(uri) {
return [{ appendBitmap: uri }, CUT_PAPER]
}
So the goal is to generate the array of commands and pass that to the queue as a job. Now, I could just do newPrintJob(printImage(uri)) in the above case, which works completely fine. However, there is a particular setting the user can configure where it will need to print multiple images, one per ticket (in other words, multiple printImages). I want to consider all of that one job, hence the need to create the printJob array.
THE PROBLEM:
I'm getting an error TypeError: Attempted to assign to readonly property which seems to be triggered by printJob.push(...printImage(uri)). If I comment that line out, the error doesn't get thrown.
I don't understand why this would happen because you can call push on an array, even if it's declared as a constant. I also tried declaring it with var and let and still received the same error.
I hope I've provided enough context here. LMK if I need to add more.
Additional info:
"react": "16.13.1"
"react-native": "~0.63.3"

Answer 1

Turns out the issue was not pushing to the array. The issue was was trying to add the job to the queue:
newPrintJob(printJob)
...outside of the async's callback. Solution was to move the newPrintJob line into the .then block.