Node.js：使用回调合并功能

Question

For these two functions :

  function isSuspended (status){
    if(status  === 'suspended'){
        return true;
    }
    return false;
 }


 function isSubscribed(status){
    if(status  === 'subscribed'){
        return true;
    }
    return false;
 }

Using Nodejs :

1- How can i merge both functions into one function with callback?

2- What is the benefit of using callbacks in such situation?

Answer 1

Here you don't need to use a callback, you can simply merge them in the following manner:

 function isSuspendedOrSubscribed(status) { return (status === 'suspended') || (status === 'subscribed'); } console.log(isSuspendedOrSubscribed('suspended')); console.log(isSuspendedOrSubscribed('subscribed')); console.log(isSuspendedOrSubscribed('random')); 

Use callback when a certain action needs to be performed after a certain event happened. For instance:

 setTimeout(()=> console.log('I am needed as a callback function to be executed after the timer') ,1000) 

Thus could also be useful for things like reaching out to the web or connecting to a database (async operations)

Answer 2

Callback in Nodejs is used to handle the asynchronous activities of the function. A callback function is called at the end of the completion of the task.

In your case we don't need callback but if you want then we can use callback like:

/*Here `status` could be `suspended` or `subscribed` and 
callback is an function reference for calling 
argumentative function which is available as a `handleSuspendOrSubscribe` parameter.*/

let handleSuspendOrSubscribe = (status, callback)=>{

 if(status == 'suspended' || stataus == 'subscribed'){
     callback(null, true);  // callback first parameter must be error and 2 must be success, It is called `error first callback`

 }else{
     callback(true, null);
 }
}

Now I am going to call handleSuspendOrSubscribe function like

handleSuspendOrSubscribe('suspended', function(err, success){
    err ? console.log('Error: ', err) : console.log('Success: ', success);
})