How can I make a program wait for a variable change in javascript?

Question

I want to force a JavaScript program to wait in some particular points of its execution until a variable has changed. Is there a way to do it? I have already found an extens

Answer 1

You can use properties:

Object.defineProperty MDN documentation

Example:

function def(varName, onChange) {
    var _value;

    Object.defineProperty(this, varName, {
        get: function() {
            return _value;
        },
        set: function(value) {
            if (onChange)
                onChange(_value, value);
            _value = value;
        }
    });

    return this[varName];
}

def('myVar', function (oldValue, newValue) {
    alert('Old value: ' + oldValue + '\nNew value: ' + newValue);
});

myVar = 1; // alert: Old value: undefined | New value: 1
myVar = 2; // alert: Old value: 1 | New value: 2