Carriage return in strings with Node.js

I wrote the following code in Node.js:

sitemap.selection = "n";
for (const deck in series) {
  sitemap.selection += `abcn`
}
console.log (sitemap)

When I run the code, it displays the following in the console:

selection: 'n' +
    'abcn' +
    'abcn' +
    'abcn' +
    'abcn' +
    'abcn' +
    'abcn' +
    'abcn'

Why the string are not concatenated?