JavaScript也有getter/setter方法：ES5 Object对象的5个不为人知的特性

1. ECMAScript 5有getter和setter属性方式

var obj = {
    get foo() {
        return Math.random();
    },
    set foo(value) {
        console.log('SET foo = '+value);
    },
};

> obj.foo
0.6029663002118468
> obj.foo
0.99780507478863
> obj.foo = 123;
SET foo = 123

2 以逗号结尾是合法的

var translations = {
    yes: 'ja',
    no: 'nein',
    perhaps: 'vielleicht',
};

3. 对象的属性通常不需要使用引号

var obj = {
    '#§$%': true,
    " \t\n": true,
};

var obj = {
    π: true,
    привет: true,
    café: true,
    $$$: true,
};

var obj = {
    1e2: true,
    1e-2: true,
    .234: true,
    0xFF: true,
};

> Object.keys(obj)
[ '100', '255', '0.01', '0.234' ]

> obj.0xFF
SyntaxError: Unexpected token
> obj[0xFF]
true

4. 你可以使用保留字作为key

> var obj = { 'new': 123 };
> obj['new']
123

> var obj = { new: 123 };
> obj.new
123

5. 使用objects作为dictionary（键值对）有一些坑

> var data = { hasOwnProperty: true };
> data.hasOwnProperty('someKey')
TypeError: boolean is not a function

> var data = {}; // empty dictionary
> 'toString' in data
true
> data.toString
[Function: toString]

function escapeKey(key) {
    // Escape '__proto__', its escaped version etc.
    if (key.indexOf('__proto__') === 0) {
        return key+'%';
    } else {
        return key;
    }
}

function getValue(obj, key) {
    return obj[escapeKey(key)];
}

function setValue(obj, key, value) {
    obj[escapeKey(key)] = value;
}

> var dict = Object.create(null);
> dict.foo = 123;
> 'toString' in dict
false
> dict.toString
undefined
> 'foo' in dict
true