Variables that are declared inside a block but used outside of it (which is possible with a var-style declaration) should be declared outside the block.

Noncompliant Code Example

function doSomething(a, b) {
  if (a > b) {
    var x = a - b;  // Noncompliant
  }

  if (a > 4) {
    console.log(x);
  }

  for (var i = 0; i < m; i++) { // Noncompliant, both loops use same variable
  }

  for (var i = 0; i < n; i++) {
  }

  return a + b;
}

Compliant Solution

function doSomething(a, b) {
  var x;

  if (a > b) {
    x = a - b;
  }

  if (a > 4) {
    console.log(x);
  }

  for (let i = 0; i < m; i++) {
  }

  for (let i = 0; i < n; i++) {
  }


  return a + b;
}