Object.watch() for all browsers?

Question

Please note that Object.Watch and Object.Observe are both deprecated now (as of Jun 2018).

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I was looking for an easy way to monitor an object

Answer 1

Current Answer

Use the new Proxy object, which can watch changes to it's target.

let validator = {
    set: function(obj, prop, value) {
        if (prop === 'age') {
            if (!Number.isInteger(value)) {
                throw new TypeError('The age is not an integer');
            }
            if (value > 200) {
                throw new RangeError('The age seems invalid');
            }
        }

        // The default behavior to store the value
        obj[prop] = value;

        // Indicate success
        return true;
    }
};

let person = new Proxy({}, validator);

person.age = 100;
console.log(person.age); // 100
person.age = 'young'; // Throws an exception
person.age = 300; // Throws an exception

Old answer from 2015

You could have used Object.observe() from ES7. Here's a polyfill. But Object.observe() is now cancelled. Sorry people!