它是否提高了存储值的性能，而不是在数组中访问它

Question

例如，这两个片段之间存在性能差异：

var my_array = [''];
for (var i = 0; i < 2000; i++) {
    my_array[0] += i;
}

和

var my_array = [''];
var my_string = array[0];
for (var i = 0; i < 2000; i++) {
    my_string += i;
}

谢谢！

Answer 1

亲自看看（越低越好）。

＆＃13;

＆＃13;

var suite = [
function test0() {
  var t0, t1;
  
  t0 = performance.now();

  var my_array = [''];
  
  for (var i = 0; i < 2000; i++) {
    my_array[0] += i;
  }
  
  t1 = performance.now();
  
  return t1 - t0;
},
function test1() {
  var t0, t1;
  
  t0 = performance.now();

  var my_array = [''];
  var string = my_array[0];
  
  for (var i = 0; i < 2000; i++) {
    string += i;
  }
  
  my_array[0] = string;
  
  t1 = performance.now();
  
  return t1 - t0;
}];

var tests = [0, 0];
var amount = [1000, 1000];

function run(test) {
  if (amount[test]-- > 0 && test < 2) {
    tests[test] += suite[test]();
    setTimeout(function(){run(test)}, 0);
  } else if (test < 1) {
    document.write('<pre>Running test 1 in 1 second</pre>');
    setTimeout(function(){
      document.write('<pre>Running test 1</pre>');
      run(test+1)
    }, 1000);
  } else {
    document.write('<pre>1000 runs complete</pre>');
    document.write('<pre>Test 0 total: ' + tests[0] + 'ms</pre>');
    document.write('<pre>Test 1 total: ' + tests[1] + 'ms</pre>');
  }
}

setTimeout(function(){
  document.write('<pre>Running test 0</pre>');
  run(0);
}, 1000);

＆＃13;

＆＃13;

＆＃13;