const arrays = new Array(1000).fill(null).map((_, j) => new Array(50).fill(null).map((_, i) => i + j));
let arr = [];
for(const array of arrays){
arr.push(...array);
}
let arr = arrays.flat();
let arr = [];
for(const array of arrays){
arr = arr.concat(array);
}
let arr = [];
for(let i = 0; i < arrays.length; i++){
arr.push(...arrays[i]);
}
let arr = [].concat(...arrays);
let arr = [].concat.apply([], arrays);
let arr = arrays.reduce((acc, array) => acc.concat(array), []);