<script>
var bar=function(){
   var foo=function(){}
   foo=10;
}
var foo=1;
bar();
alert(foo);
</script>

The js declaration part is placed on top, and the foo inside the function is a local variable and does not affect the global foo.

1 Function declaration will be at the top

2 Variable declaration will also be at the top
3 Function declaration will be at the top than variable declaration:)
4 Variables and assignment statements are written together. When parsed by the js engine, they will be split into two parts: declaration and assignment. , the declaration is at the top, and the assignment remains at the original position
5Declared variables will not be declared repeatedly

If you refer to the above points, you will understand the reason!

The actual effect of your code is:

function bar(){
 function foo(){}
  var foo;//实际上无效
  foo=10;
}
var foo;
bar();
foo=1;
console.log(foo);