我使用JavaScript解析器生成器JISON为我的用户创建的一些脚本创建解析器。最近，我注意到Firefox上的解析过程比我页面支持的任何其他浏览器（IE10、最新版Chrome和Opera）都要慢得多。
在深入挖掘生成的解析器源代码后，我将问题缩小到了一行代码，该代码执行一些正则表达式来标记要解析的代码。当然，这行代码经常被执行。
我创建了一个小的测试用例，其中包含一些随机字符串（大约1300个字符长）和一个非常通用的正则表达式。这个测试用例测量了执行10000次正则表达式的平均时间（JSFiddle上的工作示例）：
$(document).ready(function() {
var str = 'asdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj ölkasjd flöaksjdf löask dfjkasdfasdfa asdfasdf asdf asdf asdfasödlfkja asldfkj asdölkfj aslödkjf aösldkfj',
regex = new RegExp('^([0-9])+'),
durations = [],
resHtml = 'Durations:',
totalDuration = 0,
matches, start;
// Perform "timing test" 10 times to get some average duration
for (var i = 0; i < 10; i++) {
// Execute regex 10000 times and see how long it takes
start = window.performance.now();
for (var j = 0; j < 10000; j++) {
regex.exec(str);
}
durations.push(window.performance.now() - start);
}
// Create output string and update DIV
for (var i = 0; i < durations.length; i++) {
totalDuration += durations[i];
resHtml += '<br>' + i + ': ' + (parseInt(durations[i] * 100, 10) / 100) + ' ms';
}
resHtml += '<br>==========';
resHtml += '<br>Avg: ' + (parseInt((totalDuration / durations.length) * 100, 10) / 100) + ' ms';
$('#result').html(resHtml);
});
以下是我的机器上的测试结果：
Firefox 24：10000个正则表达式执行的平均时间在370和450毫秒之间。
Chrome 30、Opera 17、IE 10：平均时间在0.3到0.6毫秒之间。
如果要测试的字符串更大，这种差异会变得更加显著。一个6000个字符长的字符串会使Firefox的平均时间增加到约1.5秒！而其他浏览器仍然只需要约0.5毫秒！ （在JSFiddle上有6000个字符的工作示例）
为什么Firefox与所有其他浏览器之间存在如此巨大的性能差异？我能否以任何方式改进它？
请注意，我不能调整执行的正则表达式本身，因为它们大多是由解析器生成器生成的，我不想手动更改构建解析器的代码。