Javascript Hoisting and Additional Features

Question

Good day all,

This is not a specific question, but a general one.

In particular, i am preparing for a Javascript related interview. On Glassdoor, I saw someone mention that previously, "What is Javascript hoisting?" was a question that was asked.

In essence, I wanted to know what type material I should study on Javascript to know it to that depth.

Now, ideally, you would tell me to read a book and learn as much about Javascript such as if I were to be asked what hoisting was, that I would be able to answer it "naturally."

However, this raised an important thought with me, in that I know I have a limited amount of hours, and being able to study "smart" for interviews would be a good skill for future interviews, that may not necessarily test Javascript knowledge.

Is hoisting considered a "feature" of Javascript? What are such phenomena called, and are there books that specifically highlight the key features of a language that distinguish it from most others.

This is a very vague questions, but in essence I want to find out a way where I can learn about in-depth features of a programming language without having to study from square one, up to that point.

Hope that made sense!

Best regards, Andy

Answer 1

I guess you could call it a feature. Back in the day, you needed to make sure you defined every function before it was called, and everything would be compiled in the order it was written: Think about something like var myCat = new Cat(); function Cat() { ... }, the code would throw an error at the new Cat() token (something like undefined is not a constructor), because, at the time new Cat() is executed, the Cat function is never defined. It's defined later in the code.

With hoisting, variable declarations are loaded into memory at compile time, and you can initialize and use variables/functions before they're declared, meaning you don't have to worry about this conflict. That's really all there is to it. It's effectively a compile-time optimization - something to make peoples' lives easier, like how for (var i = 0; i < array.length; i++) array iterations are largely deprecated (outside of closure compiled code etc.) because of the Array.prototype.forEach builtin.

You can read more about function hoisting on MDN's Web Docs.

// call to catName before declaration
catName("Chloe");

function catName(name) {
  console.log(`My cat's name is ${name}!`);
}