左右两边必须一样???? 也可以不一样

  1. //常规赋值
  2. let arr = [1,2,3]
  4. let a = arr[0]
  5. let b = arr[1]
  6. let c = arr[2]
  8. console.log(a,b,c) // 1 2 3
  10. //解构赋值
  11. let arr = [1,2,3]
  12. let [a,b,c] = arr  // [a,b,c] = [1,2,3]
  13. console.log(a,b,c) // 1 2 3
  15. //右边比左边多
  16. let [a,b,c,d] = [1,2,3,'4',5]
  17. console.log(a,b,c,d) //1 2 3 "4"
  18. //左边比右边多
  19. let [a,b,c,d] = [1,2,3]
  20. console.log(a,b,c,d) //1 2 3 undefined
  22. //json对象
  23. let {a,b,c} = {a:1, d:'d', e:3}
  24. console.log(a,b,c) //1 undefined undefined 这个是错的，key 是不一样的
  26. let {a,b,c} = {a:1, b:'b', c:3}
  27. console.log(a,b,c) //1 "b" 3 这个是对的，所以，左右必须一样，key一样
  29. let {c, a, b} = {b:'b', c:3 , a:1}
  30. console.log(a,b,c) //1 "b" 3 这样也对，json对象的key是无序的
  32. //还可以这样，只要key一样就行，左右可以不一样多
  33. let {a,b,c,e,f} = {a:[1,2,3], b:'b is a string', c: {a:1,b:2,c:3}, d:0, e:999}
  34. console.log(a,b,c,e,f) 
  35. //(3) [1, 2, 3] "b is a string" {a: 1, b: 2, c: 3} 999 undefined

右边必须是个合法的东西

声明和赋值不能分开

  1. //必须写在一行，下面的是不行的
  2. let [a,b]
  3. [a,b] = [1,2]
  4. console.log(a,b)
  5. //Uncaught SyntaxError: Missing initializer in destructuring declaration