<p ng-controller="TextareaCtrl">
    <textarea ng-model="text" ng-change="checkText()"></textarea>
</p>

function TextareaCtrl($scope)
{
    $scope.checkText = function () {
        if ($scope.text.length > 5) {
            alert("text is too long");
            $scope.text = $scope.text.substr(0, 5);
        }
    };
}

Use $watch

javascript$scope.content; //假设这是你textarea上的绑定
var limitation = 150; // 假设文本长度为 150
$scope.$watch('content', function(newVal, oldVal) {
    if (newVal && newVal != oldVal) {
        if (newVal.length >= limitation) {
            $scope.content = newVal.substr(0, limitation); // 这里截取有效的150个字符
        }
    }
})

You can do this:
Bind a variable ng-model="length" to the textarea to count your current word count, and then bind a variable through ng-disabled="length>=140" to make the textarea disabled, or a pop-up box or something, anyway It is to monitor the word count of the output box.

<p ng-controller="myNoteCtrl">

<textarea ng-model="message" cols="40" rows="10" maxlength="{{ max }}"></textarea>
<p>
    <button ng-click="save()">保存</button>
    <button ng-click="clear()">清除</button>
</p>
<p>Number of characters left: <span ng-bind="left()"></span></p>    

</p>

<script>

var app = angular.module("myNoteApp", []);
app.controller("myNoteCtrl", function($scope) {
    $scope.max = 100;
    $scope.message = "";
    $scope.left  = function() {
        return 100 - $scope.message.length;
    };
    $scope.clear = function() {$scope.message = "";};
    $scope.save  = function() {alert("Note Saved");};
});

</script>