javascript ES6中箭头函数注意细节小结

x => x * x

function (x) {
return x * x;
}

const numbers = [1, 2, 3];
 const result = numbers.map(n => n * 2);
 // produces [2,4,6]

const numbers = [1, 2, 3];
 const result = numbers.map(n => { value: n });
 // produces [undefined], [undefined], [undefined]

const result = numbers.map(n => ({ value: n }));
 // [{value: 1}, {value:2}, {value:3}]

const adder = {
  sum: 0,
  add(numbers) {
   numbers.forEach(n => {
    this.sum += n;
   });
  }
 };
 adder.add([1, 2, 3]);
 // adder.sum === 6

const adder = {
  sum: 0,
  add: (numbers) => { // scope here is important
   numbers.forEach(n => {
    this.sum += n;
   });
  }

 };

 adder.add([1, 2, 3]);
 // adder.sum === 0