#TIL : Define property of an object in hacking way

Jan 7, 2018 4 mins read

Define property of an object in hacking way

Sometimes, we want to define a property of an advanced object (has setter and getter function).

Now, we could use this helper function Object.defineProperty to define property of an object in a cool way.

Example :

const foo = {};

Object.defineProperty(a, 'bar', {
	value: 'hogehoge',
	writable: false,
});

console.log(foo.bar); // 'hogehoge'
foo.bar = 'foo bar'; // throw an error in strict mode
console.log(foo.bar); // still be 'hogehoge'

Modifying setter, getter function

// Get callstack which function is getting or setting cookie value
Object.defineProperty(document, 'cookie', {
	get: function() {
		console.log('get !');
		console.trace();
	},
	set: function(val) {
		console.log('set = ', val);
		console.trace();
	},
}); 
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