ES6中有三个大而重要的数组方法 map,filter,reduce

// map 方法，对数组进行循环操作 并传入一个新的数组
const movements = [200, 450, -400, 3000, -650, -130, 70, 1300];
const eurToUsd = 1.1;
// const movementsUSD = movements.map(function (mov) {
//   return mov * eurToUsd;
// });
const movementsUSD = movements.map(mov => mov * eurToUsd);
console.log(movements);
console.log(movementsUSD);

const movementsUSDfor = [];
for (const mov of movements) movementsUSDfor.push(mov * eurToUsd);
console.log(movementsUSDfor);

const movementsDescriptions = movements.map(
  (mov, i) =>
    `Movement ${i + 1}: You ${mov > 0 ? 'deposited' : 'withdrew'} ${Math.abs(
      mov
    )}`
);

// filter()过滤器
const movements = [200, 450, -400, 3000, -650, -130, 70, 1300];
// 也能使用三个参数  第一个数值，第二个索引，第三个数组本身
const deposits = movements.filter(function (mov, i, arr) {
  return mov > 0;
  // 不符合条件的将会被过滤，符合条件的进入新的数组
});
// 好处是可以链接其他方法，可混合字符串方法和数组方法
console.log(movements);
console.log(deposits);

const depositsFor = [];
for (const mov of movements) if (mov > 0) depositsFor.push(mov);
console.log(depositsFor);

const withdrawals = movements.filter(mov => mov < 0);
console.log(withdrawals);