函数参数的默认值

  1. // demo1
  2. // ES5
  3. function log(x, y) {
  4.   y = y || 'World';
  5.   console.log(x, y);
  6. }
  8. log('Hello');
  9. log('Hello', 'China');
  10. log('Hello', '');
  12. // ES6
  13. function log(x, y = 'World') {
  14.   console.log(x, y);
  15. }
  16. log('Hello');
  17. log('Hello', 'China');
  18. log('Hello', false);
  1. // 实例1
  2. function Point(x = 0, y = 0) {
  3.   this.x = x;
  4.   this.y = y;
  5. }
  7. var p = new Point();
  8. console.log(p);
  10. // 与解构赋值默认值结合使用
  11. function foo({ x, y = 5 }) {
  12.   console.log(x, y);
  13. }
  15. foo({});
  16. foo({ x: 1 });
  17. foo({ x: 1, y: 2 });
  18. foo();

rest 参数，用于获取多余的参数，形式为(“…变量名”)

  1. // demo1
  2. function add(...values) {
  3.   let sum = 0;
  4.   for (var val of values) {
  5.     sum += val;
  6.   }
  7.   return sum;
  8. }
  10. add(2, 3, 4, 5);
  1. // demo2 rest代替arguments
  2. // 数组排序 arguments变量的写法
  3. function sortNumbers1() {
  4.   return Array.prototype.slice.call(arguments).sort();
  5. }
  7. // 数组排序 rest参数的写法
  8. const sortNumbers2 = (...numbers) => numbers.sort();
  1. // demo3 替代数组的apply方法
  2. function f(x, y, z) {
  3.   //...
  4. }
  5. var args = [0, 1, 2];
  6. f.apply(null, args);
  8. //ES6的写法
  9. function f1(x, y, z) {
  10.   //...
  11. }
  12. var args1 = [1, 2, 3];
  13. f1(...args1);
  1. // demo4 数组合并
  2. var arr1 = [0, 2, 4];
  3. var arr2 = [1, 3, 4];
  4. Array.prototype.push.apply(arr1, arr2);
  6. // ES6的写法
  7. var arr3 = [9, 8, 7];
  8. var arr4 = [6, 5, 4];
  9. arr3.push(...arr4);

箭头函数

  1. const func = () => {
  2.   console.log('test');
  3. };
  5. setTimeout(() => {}, 1000);