const arr = [40, 30, 20, 10]
const arr2 = [70, 50, 80]
const arr3 = arr.concat(arr2)
console.log(arr) // [40,30,20,10]
console.log(arr2) // [70,50,80]
console.log(arr3) // [40,30,20,10,70,50,80]
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