Closure counter inside setInterval

问题

I have a function:

setInterval(function () {
        var counter = 0;
        (function() {
          counter = counter + 1;
          console.log(counter);
          })(counter)
       }, 1000)

Why does not it increment the counter? (instead, it logs 1's). How to make it log ascending numbers? (1, 2, 3, ....)

回答1:

1. You are passing an argument to your anonymous function, but you aren't assigning that argument to a variable. You forgot to put the arguments in the function definition.
2. You are creating new variables with every iteration instead of sharing the variable between them. You need to turn your logic inside out.

(function(closed_over_counter) {

  setInterval(function() {
    closed_over_counter++;
    console.log(closed_over_counter);
  }, 1000);

})(0);

Since you are using an IIFE instead of a function you can call multiple times, this is pretty pointless. You might as well just declare the variable inside the closure.

(function() {
  var counter = 0;
  setInterval(function() {
    counter++;
    console.log(counter);
  }, 1000);
})();

回答2:

You could use a function which returns a function as closure over counter.

setInterval(function(counter) {
    return function() {
        console.log(++counter);
    };
}(0), 1000);

回答3:

Obscured version of Nina Scholz's answer with arrow functions:

setInterval(((counter) => () => console.log(++counter))(0), 1000);

来源：https://stackoverflow.com/questions/51424638/closure-counter-inside-setinterval