var testVar;
for(var i=0;i<3;iPP){
    testVar=function(){
    console.log(i)
    };
}
testVar(); // 3

let testVar;
for(let i=0;i<3;iPP){
    testVar=function(){
    console.log(i)
    };
}
testVar(); // 2

testVar, instead of the current value of I, and the value of I is iPP to 3 after the end of the last loop.
but let"s for loop, the last loop, should also hold a reference to I, and this I should also be executed once after the end of the last loop, and the iPP, should also become 3. But why the output is 2.
because of the different understanding of closures, which is not the focus of this issue, I asked the question again in a different way, as follows-
testVar () returns the I value of this function when it is called, using the for loop of var, and the last loop I value is 2. Because the loop has ended when it is called, the I value needs to be iPP,. So it becomes 3;
and let"s for cycle, theoretically speaking, is also the same process, and finally we have to do iPP,. Why is it still 2?