TypeError: Cannot read property ‘toLowerCase’ of undefined error javascript [closed]

function onChatHandler(target, context, msg, self) {
if (self) { return; }

const xxs = ["asd","asdw"];
const commandName = msg.trim();
if (xxs.some(word => msg.content.toLowerCase().includes(word))) {
  const num = rollDice();
  client.say(target, `Gelen sayi ${num}`);
  console.log(`* Bu ${commandName} komut kullanildi.`);
 
}

TypeError: Cannot read property ‘toLowerCase’ of undefined error

Answer

String.prototype.toLowerCase is for a string. Value prototypes don’t work on an undefined value (e.g: undefined.forEach or undefined.keys), nor do they work for values that don’t belong to that prototype of that value (e.g: "string".push).

This error means that you are calling .toLowerCase on a value that is undefined, so, using logic we can conclude that msg.content is undefined.

To fix it, I recommend some debugging (try to console.log msg if you can, and see what it contains).