When I run my node js app, Heroku reports an error:

/app/node_modules/discord.js/src/rest/APIRequest.js:34
agent ?? = new https.Agent ({... this.client.options.http.agent, keepAlive: true});

SyntaxError: Unexpected token '?? ='

The problem is that even if I comment out this line or delete it, the problem is not solved. And the error will prevent me from running the code.

As far as I understand, this is a new symbol for node js, which is inconsistent with heroku's version of node js, but this is just guesswork. So how do I fix this? Thanks in advance