Return index value from filter method javascript

I have an array of objects in my angular controller.

I want to return the value of the index of the field within the array which has a matching ID to my parameter.

There will only be one object in the array with a matching fieldId..

$scope.indexOfField = function(fieldId) {
  return $scope.model.fieldData.filter(function(x) {
    if (x.Id === fieldId) return // ???????
  });
}

Answer

You can’t return index from filter method.

The filter() method creates a new array with all elements that pass the test implemented by the provided function.

You can use forEach

$scope.indexOfField = function(fieldId) {
    var i;
    return $scope.model.fieldData.forEach(function(x, index) {
        if (x.Id === fieldId) {
            i = index;
        }
    });
    // use i
}

or even better to use for as you can’t stop forEach when you have found your id.

$scope.indexOfField = function(fieldId) {
    var fieldData = $scope.model.fieldData, 
        i = 0, ii = $scope.model.fieldData.length;
    for(i; i < ii; i++) if(fieldData[i].Id === fieldId) break;
    // use i
}