Guaranteeing Function Scope Expansion

After writing some code that is currently running, my next challenge involves re-factoring and tackling an issue related to scope. Specifically, I am working on retrieving message data and attempting to modify it in a more efficient manner:

function handleMessage(message) {
if(message.includes('dns')) {
    // Extracting and reorganizing the desired data for API use
    var buf1 = Buffer.allocUnsafe(26);
    buf1 = message;
    buf2 = buf1.slice(13, buf1.length);
    message = buf2.toString('ascii', 0, buf2.length);

    /* There might be a better approach using the Slack API in the future,
    but this method works well for now.
    Returns URL as a string without extra formatting.*/
    var n = message.indexOf('|');
    var o = message.indexOf('>');
    var n = n+1;
    var o = o-2;
    var s1 = message.substr(n, o);
    var p = s1.indexOf('>');
    var s2 = s1.substr(0, p);
    message = s2;
    dnsLookup(message);

} else if(message.includes(' whois')) {
    // Extracting and reorganizing desired data for API usage
    var buf1 = Buffer.allocUnsafe(26);
    buf1 = message;
    buf2 = buf1.slice(13, buf1.length);
    message = buf2.toString('ascii', 0, buf2.length);

    var n = message.indexOf('|');
    var o = message.indexOf('>');
    var n = n+1;
    var o = o-2;
    var s1 = message.substr(n, o);
    var p = s1.indexOf('>');
    var s2 = s1.substr(0, p);
    message = s2;
    whoisLookup(message);
}

It's clear that there's repetition in the above code segment, and to address this, my goal is to create two separate functions from it. However, when trying to implement these functions within the existing function, it seems like the variable being passed isn't getting updated permanently (when checking the results of the first function before the second begins, it appears unchanged).

Is there a different perspective or approach I should consider in this situation? While combining everything into one function is an option, I'm aiming to prepare for potential future scenarios.

This is the revised version with my modifications included:

function handleMessage(message) {
function removeID(message) {
    var buf1 = Buffer.allocUnsafe(26);
    buf1 = message;
    buf2 = buf1.slice(13, buf1.length);
    message = buf2.toString('ascii', 0, buf2.length);

    console.log(message);
    }
function removeSlackURL(message){
    console.log("test");
    console.log(message);
    var n = message.indexOf('|');
    var o = message.indexOf('>');
    var n = n+1;
    var o = o-2;
    var s1 = message.substr(n, o);
    var p = s1.indexOf('>');
    var s2 = s1.substr(0, p);
    message = s2;

}
if(message.includes('dns')) {
    // Take the data I want and re-organize for the API to use
    // This removes the user ID text <@XXXXXXXXX>


    removeID(message);
    removeSlackURL(message);

Answer №1

When you provide a message as an argument to a function, you are essentially passing a reference to the string to another variable that only exists within that specific function's scope. If you decide to assign a different string to the message variable inside the function, it simply updates the reference to point to the new value without impacting the original message in any way. This concept can be illustrated with this example:

var x = 2;
var y = x; //y = 2
y = 3;
console.log(x); //2

In this scenario, x represents your initial message passed onto a variable named message within the function, which is similar to how y behaves.

To ensure that changes persist, it's recommended to return the modified string from each function and utilize the returned value to update the original one.

function handleMessage(message){
  function removeID(message){
     ....
     ....
     return buf2.toString('ascii', 0, buf2.length);
  }

  function removeSlackURL(message){
     console.log("test");
     console.log(message);
     var n = message.indexOf('|');
     var o = message.indexOf('>');
     var n = n+1;
     var o = o-2;
     var s1 = message.substr(n, o);
     var p = s1.indexOf('>');
     var s2 = s1.substr(0, p);
     message = s2;
     return message;
  }

  if(message.includes('dns')) {
      // Extract necessary data and rearrange for API usage
      // Remove user ID information <@XXXXXXXXX>

      message = removeID(message);
      message = removeSlackURL(message);

  ....
  ....
  return message;
}

Answer №2

In the realm of JavaScript, variables abide by functional scope rules. Specifically, when dealing with nested functions within an outer function, there is no need to re-declare the variables already present in the outer function.

Inner functions are granted access to the variables of their enclosing outer function.

function handleMessage(message) {
  function removeID() {
    var buf1 = Buffer.allocUnsafe(26);
    buf1 = message;
    buf2 = buf1.slice(13, buf1.length);
    message = buf2.toString('ascii', 0, buf2.length);

    console.log(message);
  }
  function removeSlackURL(){
    console.log("test");
    console.log(message);
    var n = message.indexOf('|');
    var o = message.indexOf('>');
    var n = n+1;
    var o = o-2;
    var s1 = message.substr(n, o);
    var p = s1.indexOf('>');
    var s2 = s1.substr(0, p);
    message = s2;

  }
  // applying logic for both scenarios
  removeID();
  removeSlackURL();
  if(message.includes('dns')) {
    // Extract and organize data for API usage
    // Including removal of user ID text <@XXXXXXXXX>
  } else if (message.includes()) {

  }
}

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