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JavaScript

Natacha Romano
Natacha Romano
6,850 Points

I'm confused about var, let, const

I didn't understand the difference of var, let and const, i think it wasn't explained on the course, if anyone can explain it to my i really appreciate :)

2 Answers

Steven Parker
Steven Parker
229,968 Points

The "var" keyword declares variables in the scope of the current function, or with global scope outside of a function. But "let" declares variables in the scope of the current code block instead.

So, for example, when writing a conditional block inside a function, a variable declared with "var" would be available anywhere in the function. But a variable declared with "let" would only be available inside the conditional:

function test(x) {
  if (x > 0) {
    var vee = 1;
    let ell = 2;
    console.log(vee);  // 1
    console.log(ell);  // 2
  }
  console.log(vee);    // 1
  console.log(ell);    // ReferenceError: ell is not defined
}

test(1);
console.log(vee);      // ReferenceError: vee is not defined
console.log(ell);      // ReferenceError: ell is not defined

And "const" is just like "let" except that once it has been assigned, it cannot be assigned again.

And one other difference: anything declared with "var" is hoisted, but things declared with "let" or "const" are not.

Hi Natacha. The overly simple explanation would be that let and var are essentially the same, but let has become the new standard. Const is used when declaring a variable whose value will not change. There is a short course that covers these things as well as arrow function syntax and template literals. Here's a link.

https://teamtreehouse.com/library/getting-started-with-es2015-2

Hope this helps!