How to use $timeout service for asynchronous operations in AngularJS

In AngularJS, the $timeout service is used to execute a function after a specified delay. It's often used for delaying the execution of code or for triggering code asynchronously after a certain time interval. Here's how you can use $timeout for asynchronous operations in AngularJS:

1. Inject $timeout Service: Make sure to inject the $timeout service into your controller, service, or wherever you need to use it.

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   angular.module('myApp').controller('MyController', function($scope, $timeout) {
       // Controller code here
   });
   

2. Basic Usage: Call the $timeout function with a callback function as the first argument and the delay (in milliseconds) as the second argument. This callback function will be executed after the specified delay.

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   $timeout(function() {
       // Code to be executed after delay
   }, 1000); // 1000 milliseconds (1 second) delay
   

3. Returning a Promise: $timeout can also return a promise, which resolves when the specified delay has elapsed. This can be useful for chaining asynchronous operations or executing code after the delay.

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   $timeout(function() {
       // Code to be executed after delay
       // This will execute after 1 second
   }, 1000).then(function() {
       // Code to be executed after the timeout function completes
       // This will execute after the above code executes
   });
   

4. Canceling a Timeout: $timeout returns a promise, which can be used to cancel the timeout before it occurs using the cancel() method.

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   var timeoutPromise = $timeout(function() {
       // Code to be executed after delay
   }, 1000);
   
   // Cancel the timeout
   $timeout.cancel(timeoutPromise);
   

Remember, $timeout is wrapped in the AngularJS digest cycle, so any changes made to AngularJS models within the $timeout function will trigger a digest cycle and update the UI accordingly.

Here's a basic example demonstrating the use of $timeout in a controller:

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angular.module('myApp').controller('MyController', function($scope, $timeout) {
    $scope.message = "Initial Message";

    $timeout(function() {
        $scope.message = "Message after delay";
    }, 2000); // Change message after 2 seconds
});

In this example, the message will change to "Message after delay" after 2 seconds.