Property assessor (getter/setter) in JavaScript

作者:hax 的 Blog

Is property assessor good or evil? C# thinks good and Java as contrast. What about JavaScript? Maybe yes, Maybe no...

Mozilla SpiderMonkey introduce variety of solutions for getter and setter. Here is the sample:

<html>
<head>
<script type="text/ecmascript">
function trace(msg) {
document.getElementById(''''console'''').innerHTML += msg + ''''<br />'''';
}
</script>
</head>
<body>
<div id="console" class="debug"></div>
<script type="text/ecmascript" src="test-js-getset.js">
</script>
</body>
</html>

test-js-getset.js
=================

function test1() {
	
	var obj = {
		prop getter: function () { return ''''prop1''''; }
	};
	trace(obj.prop);
	
	obj.prop getter = function () { return ''''prop2''''; }
	trace(obj.prop);
	
	obj.prop getter = getter function () { return ''''prop3''''; }
	trace(obj.prop);
	
}

function test2() {
	
	function MyObj() {
		this.__defineGetter__(''''prop'''', function () { return ''''prop1''''; });
	}
	
	var obj = new MyObj();
	trace(obj.prop);
	
	obj.__defineGetter__(''''prop'''', function () { return ''''prop2''''; });
	trace(obj.prop);
	
}

function test3() {
	var obj = {
		foo: null,
		get prop() { return ''''prop1''''; },
		set prop(v) { trace(v); },
		bar: null,
	};
	trace(obj.prop);
	obj.prop = ''''hello'''';
}

test1();
test2();
test3();

Unfortunately, M$ IE supports no one of above. And even codes of test1() and test3() will cause syntax error. Only test2() can be interpreted by IE, u can catch the exception for the absence of __defineGetter__. But nothing else can u do, because I found no solution of emulating __defineGetter__ in IE, though there are some tricks to make a object with properties via wrap vbscript or introduce htc.