JS 模拟 Array.prototype.flat

简易模拟数组的 flat 方法

/**
 * 将一个输入转为合理的整数
 */
const toInterger = val => {
  const num = Number(val);
  if (Number.isNaN(num)) return 0;
  if (num === 0 || !Number.isFinite(num)) return num;
  return (num > 0 ? 1 : -1) * Math.floor(Math.abs(num));
};

/**
 * 获取一个合法的长度值
 */
const toLength = val => {
  const ite = toInterger(val);
  return Math.min(Math.max(ite, 0), Math.pow(2, 32) - 1);
};

Array.prototype._flat = function() {
  const depth = typeof arguments[0] === 'undefined' ? 1 : toLength(arguments[0]);
  const result = [];
  const forEach = result.forEach;
  const flatDeep = function(a, d) {
    forEach.call(a, function(val) {
      if (d > 0 && Array.isArray(val)) {
        flatDeep(val, d - 1);
      } else {
        result.push(val);
      }
    });
  };

  flatDeep(this, depth);

  return result;
};