Common AngularJS runtime errors and how to fix them

AngularJS is a powerful framework, but developers often encounter runtime errors due to incorrect syntax, scope issues, dependency injection problems, or other misconfigurations. Below are some of the most common AngularJS runtime errors and how to fix them effectively.

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1. $injector:unpr – Unknown Provider

Error Message:

Error: [$injector:unpr] Unknown provider: myServiceProvider <- myService

Cause:

• This happens when a service, factory, or provider is not registered properly or is missing in the module.
• It could also be due to incorrect dependency injection.

Fix:

1. Ensure that the service is correctly registered: app.service('myService', function() { this.getData = function() { return "Hello from Service!"; }; });
2. Inject the dependency properly: app.controller('myController', ['myService', function(myService) { console.log(myService.getData()); }]);
3. For minified code, use the array notation to prevent dependency injection issues: myApp.controller('myController', ['$scope', 'myService', function($scope, myService) { $scope.data = myService.getData(); }]);

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2. $digest already in progress

Error Message:

Error: [$rootScope:inprog] $digest already in progress

Cause:

• This occurs when $digest() is triggered inside another digest cycle.
• AngularJS automatically runs a digest cycle when events, HTTP calls, or directives update the UI, so manually calling $apply() inside it can cause this error.

Fix:

1. Use $applyAsync() instead of $apply(): $scope.$applyAsync(function() { $scope.message = "Updated Message"; });
2. Check if $digest() is already in progress before calling $apply(): if (!$scope.$$phase) { $scope.$apply(); }

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3. $compile:tplrt – Template Must Have Exactly One Root Element

Error Message:

Error: [$compile:tplrt] Template must have exactly one root element

Cause:

• This error occurs when a directive’s template contains multiple root elements.

Fix:

Ensure the directive template has a single root element:

Incorrect:

template: '<h1>Title</h1><p>Paragraph</p>'

Correct:

template: '<div><h1>Title</h1><p>Paragraph</p></div>'

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4. $rootScope:infdig – Infinite $digest Loop

Error Message:

Error: [$rootScope:infdig] 10 $digest() iterations reached. Aborting!

Cause:

• This occurs when a watcher keeps triggering itself, leading to an infinite loop.
• It usually happens when $watch() modifies the watched variable inside its callback.

Fix:

1. Use $timeout instead of modifying values inside $watch: $scope.$watch('count', function(newValue, oldValue) { if (newValue !== oldValue) { $timeout(function() { $scope.count++; }); } });
2. Ensure that watched expressions do not modify themselves: $scope.$watch('data', function(newValue, oldValue) { if (newValue === oldValue) return; // Prevent unnecessary updates $scope.data = processData(newValue); });

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5. $interpolate:interr – Interpolation Error

Error Message:

Error: [$interpolate:interr] Can't interpolate: {{ value }}

Cause:

• This occurs when AngularJS fails to evaluate an expression inside {{ }} due to syntax errors or undefined variables.

Fix:

1. Ensure that the variable exists in the scope: $scope.value = "Hello, AngularJS!";
2. Check for syntax errors in expressions: <p>{{ value }}</p> <!-- Ensure there are no typos -->

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6. ngRepeat:dupes – Duplicate Key in ng-repeat

Error Message:

Error: [$compile:dupes] Duplicates in a repeater are not allowed

Cause:

• This happens when AngularJS detects duplicate objects in an ng-repeat loop.

Fix:

1. Use track by with a unique identifier: <li ng-repeat="item in items track by item.id">{{ item.name }}</li>
2. Ensure array items have unique values: $scope.items = [ { id: 1, name: "Item 1" }, { id: 2, name: "Item 2" } ];

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7. $http:badreq – Bad Request in HTTP Calls

Error Message:

Error: [$http:badreq] Bad Request

Cause:

• The $http request is missing required parameters or is improperly formatted.

Fix:

1. Ensure the request has the correct format: $http.post('/api/data', { name: "AngularJS" }) .then(function(response) { console.log(response.data); }) .catch(function(error) { console.error("Request failed:", error); });
2. Check for missing headers: $http({ method: 'POST', url: '/api/data', data: { name: "AngularJS" }, headers: { 'Content-Type': 'application/json' } });

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8. $parse:syntax – Syntax Error in Expressions

Error Message:

Error: [$parse:syntax] Syntax Error: Token 'unexpected' is unexpected

Cause:

• This occurs due to incorrect syntax in an AngularJS expression.

Fix:

1. Check for typos and missing operators: <p>{{ 5 + 5 }}</p> <!-- Correct --> <p>{{ 5 + }}</p> <!-- Incorrect -->
2. Ensure function calls in expressions are valid: $scope.getMessage = function() { return "Hello, AngularJS!"; }; htmlCopyEdit<p>{{ getMessage() }}</p> <!-- Correct -->