What is the difference between public and Local scope

Question

function b() {
  console.log(myvar);
}

function a() {
  var myvar = 2;
  console.log(myvar);
  b();
}

var myvar = 1;
console.log(myvar);
a();
console.log(myvar);

Why output of console log of myvar in function b is 1 not 2?