The book isn't quite right. Unless you deliberately concatenate with a string, the console will generally log the argument as-is. Numbers will be logged as numbers, strings will be logged as strings, objects will be logged as (expandable, navigable) objects, and so on.
console.log(20);
console.log('20');
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…