javascript - 为什么在定义带有或不带引号的 JavaScript 对象字面量时速度会有所不同？

Question

在纯 JavaScript 中，MDN和 Google JavaScript style guide建议以下两个片段是等效的:

// Snippet one
var myObject = {
  "test":"test"
}

// Snippet two
var myObject = {
  test:"test"
}

我编写了一个测试函数，它使用 performance.now() ( MDN ) 来测量创建一百万个简单对象所花费的时间:

function test(iterations) {
  var withQuotes = [];
  var withoutQuotes = [];

  function testQuotes() {
      var objects = [];
      var startTime, endTime, elapsedTimeWithQuotes, elapsedTimeWithoutQuotes;

      // With quotes
      startTime = window.performance.now();

      for (var i = 0; i < 1000000; i++) {
          objects[objects.length] = {
              "test": "test"
          };
      }

      endTime = window.performance.now();
      elapsedTimeWithQuotes = endTime - startTime;

      // reset
      objects = undefined;
      startTime = undefined;
      endTime = undefined;
      objects = [];

      // Without quotes
      startTime = window.performance.now();

      for (var i = 0; i < 1000000; i++) {
          objects[objects.length] = {
              test: "test"
          };
      }

      endTime = window.performance.now();
      elapsedTimeWithoutQuotes = endTime - startTime;

      return {
          withQuotes: elapsedTimeWithQuotes,
          withoutQuotes: elapsedTimeWithoutQuotes
      };
    }

  for (var y = 0; y < iterations; y++) {
      var result = testQuotes();
      withQuotes[withQuotes.length] = result.withQuotes;
      withoutQuotes[withoutQuotes.length] = result.withoutQuotes;

      console.log("Iteration ", y);
      console.log("With quotes: ", result.withQuotes);
      console.log("Without quotes: ", result.withoutQuotes);
  }

  console.log("\n\n==========================\n\n");
  console.log("With quotes average: ", (eval(withQuotes.join("+")) / withQuotes.length));
  console.log("Without quotes average: ", (eval(withoutQuotes.join("+")) / withoutQuotes.length));
}

test(300);

我得到的结果表明使用引号(略微)更快。为什么会这样？

在我的浏览器上，我从我的测试函数中得到了这些结果(平均超过 300 次迭代):

带引号:167.6750966666926ms
没有引号:187.5536800000494ms

当然，也有可能我的测试函数也是duff...

我的浏览器: Chrome 29.0.1547.65

Answer 1

我认为这取决于您的浏览器。性能大致相当。 http://jsperf.com/objectquotes