I'm confused about var, let, const

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.