javascript - Problem with variable assignment in timer

Question

var a=0;
var timer=setTimeout(function(){
    a++;
},1000);
if(a>0){
    alert("1");
}

I clearly changed the value of a in this code in the timer, why is the output still 0?
How should I write to make this pop-up window pop up? (Based on making the judgment effective. )

Answer 1

The execution sequence you imagined

var a = 0;
a++;
console.log(a);

Actual execution sequence

var a = 0;
console.log(a);
delay 1 second ……
a++;

There are many ways to get this a=1, but you don’t know the meaning here, what is it for.

If you have additional questions, please put them in the question, not in the comments of the question.