AngularJs $ watchGroup-組中的哪個表達式最后一次更改？

Question

使用$watchGroup ，如何確定組中的哪個表達式已更改

    $scope.$watchGroup(['dec','bin','oct','hex'], function(newValues, oldValues, scope) {
       last_changed = ??? //return which exp was changed in this run...
       if(last_changed=='dec') //then something
       if(last_changed=='bin') //then something
       if(last_changed=='oct') //then something
       if(last_changed=='hex') //then something
    });

編輯1：-
--->問題是我無法將n_vals與newValues解除綁定。

var n_vals = [];
 $scope.$watchGroup(['dec','bin','oct','hex'], function(newValues, oldValues, scope) {
  last_updated = changed_one(newValues,n_vals); //last_updated EXP
    n_vals = newValues;
 });

解：-

n_vals = angular.copy(newValues);

看下面的鏈接：
深度復制對象成角度嗎？

Answer 1

Angular提供$watchGroup （從1.3開始） 。

基本上，它以我們將其放入watchGroup的方式返回范圍變量oldValue和newValue 。

使用范圍變量的索引來獲取其各自的newVal和oldVal如下所示。

要獲取各個范圍變量的newValue ：

newValue[0] // returns new value of dec
newValue[1] // returns new value of bin
newValue[2] // returns new value of oct
newValue[3] // returns new value of hex

要獲取各個范圍變量的oldValue ：

oldValue[0] // returns old value of dec
oldValue[1] // returns old value of bin
oldValue[2] // returns old value of oct
oldValue[3] // returns old value of hex

$scope.$watchGroup(['dec','bin','oct','hex'], function(newValues, oldValues, scope) {
    console.log(newValues[index]); //put index value as 0(dec), 1(bin), 2(oct) or 3(hex)
    console.log(oldValues[index]); //put index value as 0(dec), 1(bin), 2(oct) or 3(hex)
});

注意：
下面的邏輯考慮到一次只能更改一個值。

編輯1

要捕獲最后更新的變量，可以嘗試以下代碼。

var arrayOfValues = ['dec', 'bin', 'oct', 'hex'];
$scope.$watchGroup(arrayOfValues, function(newValues, oldValues, scope) {
    let last_changed;

    var chanedIndex = newValues.findIndex(function(val, key){
        return val !== oldValues[key];
    });

    last_changed = arrayOfValues[chanedIndex];

    // above logic could simply avoid the below conditional logic (refer 
    // comment above in front of if condition)
    if (angular.isDefined(last_changed)) {
        // your logic will come here as per your question
        switch(last_changed){
           case 'dec':
               doSomething();
           case 'bin':
               doSomething();
           case 'oct':
               doSomething();
           case 'hex':
               doSomething();
        }
    }
});

編輯2：

我縮小了代碼並使

var arrayOfValues = ['dec', 'bin', 'oct', 'hex'];
// generic method which will tell you which variable has been updated
$scope.checkWhichVariableHasUpdated = fucntion(watchGroupList, newValuesObj, oldValuesObj) {
    let _lastUpdatedValue;
    angular.forEach(watchGroupList, function(value, index) {
        if (newValuesObj[index] != oldValuesObj[index])
            _lastUpdatedValue = value;
    });
    return _lastUpdatedValue;
};

$scope.mySwitchFunction = function(changedVariable) {
    switch (changedVariable) {
        case 'dec':
            doSomething();
            break;
        case 'bin':
            doSomething();
            break;
        case 'oct':
            doSomething();
            break;
        case 'hex':
            doSomething();
            break;
    }

};

$scope.$watchGroup(arrayOfValues, function(newValues, oldValues, scope) {
    var last_changed = $scope.checkWhichVariableHasUpdated(arrayOfValues, newValues, oldValues);
    if (angular.isDefined(last_changed)) {
        $scope.mySwitchFunction(last_changed)
    }
});

我希望這可以解決問題。