Errors when using/defining function in JavaScript

Question

I wrote a JS function which parses a JSON response and displays it as a toast message. Everything works fine. I am now adding an additional feature. The JSON response is in this format:

{
  "type": "message",
  "message": "Payment Approved with Order Number: &&Secure.OrderNum&& and Transaction ID: &&Secure.TransactionNum&&"
}

Instead of taking the whole message, I want to extract the variable value of TransactionNum and just display it in the HTML (so not just in the toast).

So this is the JS I wrote to extract the one value in the message object:

_onDataEvent(jsonData) {
  let eventData = JSON.parse(jsonData);

  // Is this a message?
  if (eventData.type === "message") {
    // Yes, show the status
    let message = eventData.message;
    const evt = new ShowToastEvent({
      title: "Payment Status",
      message: message,
      variant: 'info'
    });
    dispatchEvent(evt);
  }

  // Is this a result?
  else if (eventData.type === 'result') {
    // Yes, show the result
    let success = eventData.success;
    let message = eventData.message;

    const evt = new ShowToastEvent({
      title: "Payment Result",
      message: message,
      variant: success ? 'success' : "error",
      url: "www.five9.com"
    });
    transaction(message); //I added this and VS code keeps on putting a red squiggly line on it.
    dispatchEvent(evt);
  }
}

transaction(message) {
  var words = message.split(" ");
  var transactionId = words[-1];
  return transactionId;
}

Right now, I am getting errors on the when I am calling the method. It says

transaction is not defined

When I add function keyword to the method, I then don't get the red squiggly line on the method call, but I get another error saying

Unexpected token: A constructor, expression, accessor or property was expected

I am not sure how to solve this. Have I done something wrong in the method? Is the method written correctly? Do I need to add something or change the order?

Is this wrapped in a class, and/or is it Typescript by any chance? — Tyler Roper
– Tyler Roper, Commented Nov 13, 2019 at 20:52
transaction(message){ is not a valid function definition, it is lacking the function keyword. Same for your _onDataEvent(jsonData) { — Klaycon
– Klaycon, Commented Nov 13, 2019 at 20:53
@Klaycon They're valid if they're prototype methods of a class, where function myFunction() is not, hence why I'm curious if this is all wrapped in a class of some sort :) — Tyler Roper
– Tyler Roper, Commented Nov 13, 2019 at 20:54
@user3685949 What is the context of this code? Again, it sounds like your entire snippet exists within a class. — Tyler Roper
– Tyler Roper, Commented Nov 13, 2019 at 20:59
FYI words[-1] will always return undefined. Unless it has changed in some ES6+ — Thevs
– Thevs, Commented Nov 13, 2019 at 21:04

FZs · Accepted Answer · 2019-11-13 21:19:20Z

1

Your code is probably inside an object literal, or class declaration.

If you omit the function keyword, you define a method on the object (not a global scope function).
You can't use the function keyword there, as it isn't allowed.

To solve it, place the function declaration inside the _onDataEvent method, to create it locally:

_onDataEvent(jsonData) {

  function transaction(message) {
    var words = message.split(" ");
    var transactionId = words[-1];
    return transactionId;
  }

  let eventData = JSON.parse(jsonData);

  // Is this a message?
  if (eventData.type === "message") {
    // Yes, show the status
    let message = eventData.message;
    const evt = new ShowToastEvent({
      title: "Payment Status",
      message: message,
      variant: 'info'
    });
    dispatchEvent(evt);
  }

  // Is this a result?
  else if (eventData.type === 'result') {
    // Yes, show the result
    let success = eventData.success;
    let message = eventData.message;

    const evt = new ShowToastEvent({
      title: "Payment Result",
      message: message,
      variant: success ? 'success' : "error",
      url: "www.five9.com"
    });
    transaction(message);
    dispatchEvent(evt);
  }
}

Also, the transaction function does nothing useful in its current form:

It does not mutate anything
It returns a value, but the caller ignores it
You can't access array indexes from backwards using negative numbers, it will access the "-1" property instead (which is usually undefined)

But these are off-topic for this question.

edited Nov 13, 2019 at 21:19

answered Nov 13, 2019 at 20:58

FZs

18.8k13 gold badges47 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Klaycon Over a year ago

This is probably not an ideal solution, it would be easier to keep the transaction function as a method of the object/class and call it properly with this.transaction(message);

FZs Over a year ago

@Klaycon We don't know how _onDataEvent called, and as I see, it probably called from an external code. this might not point to the correct object, if it's called via call(), apply(), stored in a variable, or used bind() on it. This solution is safer, as it works in the above scenarios as well.

Klaycon Over a year ago

Good point, but in those conditions I still think I'd prefer having it outside of the class definition. Nested function definitions aren't so good for readability and maintainability

LCPunch · Accepted Answer · 2019-11-13 21:03:57Z

0

It seems that you're using your code wrapped in a class.

In this context, your this is related to the object. So if you don't use 'this' it will search just within the function context, thus giving you the error.

answered Nov 13, 2019 at 21:03

LCPunch

294 bronze badges

Collectives™ on Stack Overflow

Errors when using/defining function in JavaScript

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related