上一篇文章講了Object的解構，這篇講一下Array的解構，概念大同小異，只是寫法會有一些不同，先看個簡單的例子：

let [x, y] = ['a', 'b','c']; // x = 'a'; y = 'b'

ArrayAssignmentPattern : [ ] 

1. Let iterator be GetIterator(value). 

2. ReturnIfAbrupt(iterator). 

3. Return IteratorClose(iterator, NormalCompletion(empty

從上面的描述看，右側應該是個iterator物件，具體什麼樣的物件才能算是iterator，後面章節會詳細講，這裡就不仔細說了，先記住就好了。

let x;
[x] = {}; // TypeError, empty objects are not iterable
[x] = undefined; // TypeError, not iterable
[x] = null; // TypeError, not iterable

下面看一些陣列解構的特性：

let [x] = []; // x = undefined

var o = {},a =[];
[o.a, o.b, o.c,a[0]] = [1,2,3,4];
//o:{ a: 1, b: 2, c: 3 },a:[4]

let [x,...y] = 'abc'; // x='a'; y=['b', 'c']，rest操作符

var o = [1,2,3],
a, b, c, p;
p = [,,c] = [a,b] = o;//解構連續賦值
trace( a + " " + b + " " +c ); // 1 2 3
trace(p === o); // true

var a1 = [ 1, [2, 3, 4,7,8], 5 ];//巢狀解構+rest操作符
var [ a, [ b, c,...d], e ] = a1;
//a=1,b=2,c=3,d=[4,7,8],e=5
 

var x = 10, y = 20;
[ y, x ] = [ x, y ];//如此的優雅

//如果還藉助臨時變數，還可以用異或操作符，當然不好理解
x^=y;
y^=x;
x^=y;

let [x=3, y] = []; // x = 3; y = undefined

let [x=1] = [undefined]; // x = 1

function log(x) { trace(x+"\n"); return 'YES' }
let [a=log('hello')] = [1];//a = 1
let [a=log('hello')] = [0];//a = 'YES',注意這裡Kinoma和ES6規範的區別，在Firefox43下，a=0

let [x=3, y=x] = []; // x=3; y=3
let [x=3, y=x] = [7]; // x=7; y=7
let [x=3, y=x] = [7, 2]; // x=7; y=2

let [x=y, y=3] = []; // ReferenceError，從左到右evaluate

let [{ prop: x } = {}] = [];//x=undefined
let [{ prop: x } = {}] = [1];//x=undefined
 

let [{ prop: x } = { prop: 123 }] = [{prop:1}];//x=1

let [all, year, month, day] =/^(\d\d\d\d)-(\d\d)-(\d\d)$/.exec('2015-12-31');
//all="2015-12-31",year="2015",month="12",day="31"

let [, , , day] =/^(\d\d\d\d)-(\d\d)-(\d\d)$/.exec("test") || [];
//day=undefined，如果不寫||[]，將會報錯，因為exec返回null，而null是不能進行解構的