Checkbox state not maintained across digest cycles

If a checkbox in AngularJS loses its state (checked/unchecked) after a digest cycle, page refresh, or other UI updates, it is usually due to binding issues, incorrect scope, or improper use of ng-model.

This guide will walk you through the causes and solutions step by step to ensure the checkbox state persists correctly.

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1. Why Does the Checkbox State Reset?

Cause 1: Checkbox is Bound to a Primitive Value

• In AngularJS, primitive values (boolean, string, number) are copied into isolated scopes, which can cause binding issues.
• If a checkbox is inside ng-repeat, each iteration may create a new isolated scope, breaking two-way binding.

Cause 2: Data is Fetched Asynchronously

• If your checkbox data is retrieved from an API after the initial digest cycle, the checkbox state may reset when the data updates.

Cause 3: ng-model is Incorrectly Used

• If ng-model is bound to a temporary value (true or false) instead of an object property, the state won’t persist across updates.

Cause 4: Checkbox Inside ng-repeat Without Unique Binding

• If a checkbox inside ng-repeat lacks a unique identifier, the state may be lost when Angular re-renders the list.

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2. Fixing the Checkbox State Issues

Solution 1: Use an Object Instead of a Primitive

Fix Scope Issue Using Objects

Incorrect Usage (Primitive Binding)

<input type="checkbox" ng-model="isChecked"> Remember me

$scope.isChecked = false;

• Problem: If isChecked is inside an ng-repeat or an isolated scope, Angular creates a copy of the primitive value instead of binding to the parent scope.

Correct Usage (Object Binding)

<input type="checkbox" ng-model="formData.isChecked"> Remember me

$scope.formData = { isChecked: false };  // Using an object

Why This Works?

• Objects maintain reference integrity across digest cycles.

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Solution 2: Ensure Data is Available Before UI Renders

If the checkbox is bound to data coming from an API, the UI may not update properly.

Use ng-if to Wait for Data

<div ng-if="formData">
    <input type="checkbox" ng-model="formData.isChecked"> Remember me
</div>

setTimeout(function () {
    $scope.formData = { isChecked: true };
    $scope.$apply();  // Ensures Angular updates the UI
}, 2000);

Why This Works?

• Ensures the checkbox is only rendered after the data is available.

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Solution 3: Use $watch to Detect Changes

If data arrives asynchronously, use $watch to track changes and update the checkbox.

Example

$scope.$watch('formData.isChecked', function (newValue, oldValue) {
    if (newValue !== oldValue) {
        console.log("Checkbox state changed:", newValue);
    }
}, true);

Why This Works?

• Detects any change in checkbox state and ensures it stays updated.

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Solution 4: Handle ng-repeat Properly with Unique Bindings

If a checkbox inside ng-repeat does not persist its state, ensure each item has a unique identifier.

Incorrect Usage

<div ng-repeat="item in items">
    <input type="checkbox" ng-model="item.selected"> {{ item.name }}
</div>

$scope.items = [
    { name: "Item 1" },
    { name: "Item 2" }
];

• Problem: Since selected is missing, Angular may lose track of checkbox states.

Correct Usage

<div ng-repeat="item in items">
    <input type="checkbox" ng-model="item.selected"> {{ item.name }}
</div>

$scope.items = [
    { name: "Item 1", selected: false },
    { name: "Item 2", selected: true }
];

Why This Works?

• Each checkbox binds to a specific object property, preventing resets.

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Solution 5: Persist Checkbox State in Local Storage

If the checkbox needs to remember state after a page reload, store its value in localStorage.

Example

<input type="checkbox" ng-model="formData.isChecked" ng-change="saveState()"> Remember me

$scope.formData = { isChecked: localStorage.getItem("checkboxState") === "true" };

$scope.saveState = function () {
    localStorage.setItem("checkboxState", $scope.formData.isChecked);
};


 Why This Works?

• Saves the checkbox state even after a page refresh.