Parsing the ambiguity of square brackets "[]" in Javascript_javascript skills

Javascript square brackets have four semantics

Semantics 1, declare array

Copy code The code is as follows:

var ary = []; // Declare an empty array
var ary = [1,3]; // Declare an array and assign an initial value

Semantic 2 , take the array members

Copy code The code is as follows:

var ary = [1 ,2,3];
var item = ary[0];

Semantic 3, define object members (you can not follow identifier rules)

Copy code The code is as follows:

var obj = {};

// Add an attribute name to obj. name is a legal identifier, that is, it can also be defined through obj.name
obj['name'] = 'jack';

// Add an attribute 2a to obj. 2a is not a legal identifier (cannot start with a number) and cannot be defined by obj.2a
obj['2a'] = 'test';

Semantics 4, get object members

Copy code The code is as follows:

var obj = {name:'jack'};
obj['2a'] = 'test';

obj['name']; // --> jack
obj['2a']; // --> test (cannot be obtained through obj.2a)