Unexpected token ':' in Typescript when defining a function

I have been following examples included in "Learning Typescript" by Josh Goldberg. I am stuck in an example providing the definition of a function in Typescript:

//index.ts
let songLogger: (song: string) => void;

songLogger = (song) => {
    console.log(`${song}`);
}

songLogger("Heart of Glass");

When executing the snippet, getting the following:

PS C:\Typescript> node index.ts
C:\Typescript\index.ts:1
let songLogger: (song: string) => void;
              ^

SyntaxError: Unexpected token ':'
    at internalCompileFunction (node:internal/vm:73:18)
    at wrapSafe (node:internal/modules/cjs/loader:1178:20)
    at Module._compile (node:internal/modules/cjs/loader:1220:27)
    at Module._extensions..js (node:internal/modules/cjs/loader:1310:10)
    at Module.load (node:internal/modules/cjs/loader:1119:32)
    at Module._load (node:internal/modules/cjs/loader:960:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:23:47

Do you know what I am doing wrong? I am not finding the culprit of the syntax error.

Thanks a lot

You're using node to run the typescript. You have to first transpile to JavaScript. You can use tsc to do that.