关于性能：为什么定义带有或不带引号的JavaScript对象文字有什么不同？


Why is there a difference in defining a JavaScript object literal with or without quotations marks?

本问题已经有最佳答案，请猛点这里访问。

在纯JavaScript中，MDN和Google JavaScript样式指南建议下面的两个片段是等效的：

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

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

但是，JSON规范要求使用引号。

在定义对象文字时使用引号是否正确，如果有的话？ 这是否意味着对口译员有任何影响？

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需的时间：

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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("

==========================

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

test(300);

结果我暗示使用引号(稍微)更快。 为什么会这样？

在我的浏览器上，我从测试函数中获得了这些结果(平均超过300次迭代)：

报价：167.6750966666926ms
没有引号：187.5536800000494ms

当然，我的测试功能也是可能的...

相关讨论

A property's name can be any string, including the empty string. The
quotes around a property's name in an object literal are optional if
the name would be a legal JavaScript name and not a reserved word. So
quotes are required around"first-name", but are optional around
first_name.

资料来源：Douglas Crockford的"JavaScript：The Good Parts"。