How do sum values from an array of key-value pairs in JavaScript?

To fix getFullyear() is not a function with JavaScript, we should be called getFullYear instead.

For instance, we write

const start = new Date();
const y = start.getFullYear();

to call start.getFullYear to return the 4-digit year number of the start date.

Conclusion

To fix getFullyear() is not a function with JavaScript, we should be called getFullYear instead.