Unexpected identifier Javascript hello world

I think you are intendings to add those string values together. I'd recommend starting off the with + operator. Good luck!

let sayHelloStr = "Hello world! My name is " + firstName + " " + lastName;

You want to use concat ( + ) your variable into the string.. otherwise it will be throwing like this.

let sayHelloStr = "Hello world, My name is " + firstName + " " + lastName