ngMask directive override existing mask pattern

[Prabukmca]

We are assigning the pattern dynamically to the mask directive, when we assigning three different patterns to text boxes the last pattern is override the other mask text box patterns.

We are using ngMask.min.js

The below three textboxes are dynamically generated.

<input ng-if="field.isMaskUsed" type="text" ng-change="sdf.setNewFalse(field)" mask="9999" mask-restrict="reject" mask-clean="true" class="textField form-control ng-pristine ng-untouched ng-valid ng-empty" ng-model="field.value">

<input ng-if="field.isMaskUsed" type="text" ng-change="sdf.setNewFalse(field)" mask="@@99" mask-restrict="reject" mask-clean="true" class="textField form-control ng-pristine ng-untouched ng-valid ng-empty" ng-model="field.value">

<input ng-if="field.isMaskUsed" type="text" ng-change="sdf.setNewFalse(field)" mask="@@@@" mask-restrict="reject" mask-clean="true" class="textField form-control ng-pristine ng-untouched ng-valid ng-empty" ng-model="field.value">

The last pattern '@@@@' is override the above text box patterns and those textboxes accepting only alpha characters.

Kindly help me to resolve this issue.

Thank you