为什么执行相同的JavaScript代码所需的时间会有所不同

Question

查看控制台，每次我都不知道为什么时间会有所不同

我试图执行一个函数并获取它所花费的时间，我使用了console.time（），但是每次运行它时，它都会显示不同的时间。还有一点，下划线所花费的时间是否比正常执行时间还要长。

 function map(){ console.time('mycode'); var arr = [234345345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,5445645,456456,456456,234,467,234234234,456,43535,456,12,3123123123,456,456456,1231235,6456456,234,234456,4,5632452344,65,543452334124436,2345,345346,2345]; var result = []; var constant = 3; var length = arr.length; //will avoid calculation of length each time for(i=0;i<length;i++){ temp = arr[i] * constant; result.push(temp); } console.timeEnd('mycode'); console.time('mycode1'); var underscore = _.map([arr], function(num){ return num * 3; }); console.timeEnd('mycode1'); } function where(){ console.time("myCode"); var arr = [{title: "Cymbeline", author: "Shakespeare", year: 1611}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615}, {title: "The Tempest", author: "Shakespeare", year: 1613}, {title: "The Tempest", author: "Shakespeare", year: 1615} ]; var author = 'Shakespeare'; var year = '1611'; var result = []; var length = arr.length; //will avoid calculation of length each time for(i=0;i<length;i++){ //you know that and takes more time than or statement if(arr[i]['author'] == author && arr[i]['year'] == year){ result.push(arr[i]); } } console.log(result) console.timeEnd("myCode"); console.time("myCode1"); var underscore = _.filter(arr, {author: "Shakespeare", year: 1611}); console.log(underscore) console.timeEnd("myCode1"); } 

 .container{ width:calc(100% - 200px); text-align:center; margin:0 auto; background:#f4f4f4; } 

 <script src="http://underscorejs.org/underscore-min.js"></script> <h1>Evaluating time </h1> <input type='button' onclick='map()' value='Execute'> <input type='button' onclick='where()' value='Execute'> 

Answer 1

执行代码所需的时间将因CPU正在执行的其他工作而异。 由于计算机上正在运行其他进程，因此不断发生中断。 您的Web应用程序只是许多需要占用CPU时间的应用程序之一。 还有一些因素，例如CPU对频繁请求的数据以及OS缓存进行缓存。