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Victor Stanciu
Full Stack JavaScript Techdegree Student 11,196 PointsWhy is my variable initialized with the default value of `undefined`, if I declared it with `let` ?
Hi!
Going through the Teacher's Notes, I stumbled upon the link about Hoisting, from MDN https://developer.mozilla.org/en-US/docs/Glossary/Hoisting#let_and_const_hoisting . It says:
"Variables declared with let and const are also hoisted, but unlike for var the variables are not initialized with a default value of undefined. Until the line in which they are initialized is executed, any code that accesses these variables will throw an exception."
I typed the following lines of code directly in the console. The return is commented after each line.
var a; // returns undefined
let b; // returns undefined
const c; // returns Uncaught SyntaxError: Missing initializer in const declaration
My question is: Why is b initialized as undefined, if the documentation states that the JS engine should throw an exception? Did I misunderstand the documentation?
I reloaded the page and even tried the same lines of code in a new tab, but always get the same result.
Thanks so much for your help!
1 Answer
Steven Parker
231,269 PointsIt's a forward reference that throws the exception, not the declaration itself. For examples:
// example 1: both the declaration and initialization are hoisted:
console.log(a); // will show "undefined"
var a;
// -------------------------------------------
// example 2: only the declaration is hoisted:
console.log(b); // will cause exception
let b;
Victor Stanciu
Full Stack JavaScript Techdegree Student 11,196 PointsVictor Stanciu
Full Stack JavaScript Techdegree Student 11,196 PointsThanks! Your example helped me understand this better. I only declared the variables in my browser console, without actually trying to access (correct term?) their values with console.log.