什么在函数中创建函数？

Question

Why is the result of the following code 1 and not 10? Why doesn't the function bar() change the value, even though there is a return statement.

var foo = 1;
function bar() {
  foo = 10;
  return;

  function foo() {}
}

bar();
alert(foo);

Answer 1

This is because while compiling the foo function declaration inside bar moves on the top of the bar . Like this

var foo = 1;
function bar() {
  function foo() {}
  foo = 10;
  return;
}

bar();
alert(foo);

Read about hoisting in JS . And here in the "var hoisting" section

Answer 2

This is because function definitions are hoisted to the top of their scope, so the foo assignment inside bar() is actually referring to the local function that has an empty body.

You can read more about this here