问如何观察数组的变化？

EN

function processQ() {
   // ... this will be called on each .push
}

var myEventsQ = [];
myEventsQ.push = function() { Array.prototype.push.apply(this, arguments);  processQ();};

/* @arr array you want to listen to
   @callback function that will be called on any change inside array
 */
function listenChangesinArray(arr,callback){
     // Add more methods here if you want to listen to them
    ['pop','push','reverse','shift','unshift','splice','sort'].forEach((m)=>{
        arr[m] = function(){
                     var res = Array.prototype[m].apply(arr, arguments);  // call normal behaviour
                     callback.apply(arr, arguments);  // finally call the callback supplied
                     return res;
                 }
    });
}

// For example, take any array:
var a = ['zero', 'one', 'two', 'trhee'];

// Add a generic observer function to that array:
_.observe(a, function() {
    alert('something happened');
});