javascript-AngularJs $watchGroup-群组中的哪个表达式最后一次更改？

使用$watchGroup,如何确定组中的哪个表达式已更改

    $scope.$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
    });

编辑1：-
—>问题是我无法将n_vals与newValues解除绑定.

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);

看下面的链接：
Deep copying objects in angular?

解决方法:

Angular提供$watchGroup(从1.3开始).

基本上,它以我们将其放入watchGroup的方式返回范围变量oldValue和newValue.

使用范围变量的索引来获取其各自的newVal和oldVal,如下所示.

要获取各个范围变量的newValues：

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

要获取各个范围变量的oldValues：

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)
});

NOTE:
Below logic is considering that only one value will change at a time.

编辑1

要捕获最后更新的变量,可以尝试以下代码.

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();
        }
    }
});

编辑2：

我缩小了代码并使

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)
    }
});

我希望这可以解决问题.

标签：javascript,angularjs,angularjs-service,angularjs-watch
来源： https://codeday.me/bug/20191009/1879869.html