生成二维数组

genArray.js

function genArray(rows, cols, something) {
  // BAD! Rows are copied by reference
  // return new Array(rows).fill(new Array(cols).fill(something))
  
  // good way
  Array.from(Array(rows), () => new Array(cols).fill(something))
  
  // more inefficient 12%
  // return new Array(rows).fill(null).map(() => Array(cols).fill(something))
}