爲什麼執行相同的javascript代碼所花費的時間變化

看到控制檯的時刻變化的每個我不一次知道爲什麼爲什麼執行相同的javascript代碼所花費的時間變化

我試圖執行一個功能並獲得通過它拍攝的時候，我已經使用控制檯.time（），但每當我運行它時顯示不同的時間還有一件事，下劃線花費的時間比正常的執行時間多。

function map(){ 
 
\t \t 
 
\t \t console.time('mycode'); 
 
\t \t 
 
\t \t 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]; 
 
\t \t var result = []; 
 
\t \t var constant = 3; 
 
\t \t var length = arr.length; //will avoid calculation of length each time 
 
\t \t for(i=0;i<length;i++){ 
 
\t \t \t temp = arr[i] * constant; 
 
\t \t \t result.push(temp); 
 
\t \t } 
 
\t \t 
 
\t \t console.timeEnd('mycode'); 
 
\t \t 
 
\t \t console.time('mycode1'); 
 
\t \t 
 
\t \t var underscore = _.map([arr], function(num){ return num * 3; }); 
 
\t \t 
 
\t \t console.timeEnd('mycode1'); 
 
\t } 
 
\t 
 
\t function where(){ 
 
\t \t 
 
\t \t console.time("myCode"); 
 
\t \t var arr = [{title: "Cymbeline", author: "Shakespeare", year: 1611}, 
 
\t \t \t 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1613}, 
 
\t \t \t {title: "The Tempest", author: "Shakespeare", year: 1615} 
 
\t \t ]; 
 
\t \t var author = 'Shakespeare'; 
 
\t \t var year = '1611'; 
 
\t \t var result = []; 
 
\t \t var length = arr.length; //will avoid calculation of length each time 
 
\t \t for(i=0;i<length;i++){ //you know that and takes more time than or statement 
 
\t \t \t if(arr[i]['author'] == author && arr[i]['year'] == year){ 
 
\t \t \t \t result.push(arr[i]); 
 
\t \t \t } 
 
\t \t } 
 
\t \t console.log(result) 
 
\t \t console.timeEnd("myCode"); 
 
\t \t 
 
\t \t console.time("myCode1"); 
 
\t \t var underscore = _.filter(arr, {author: "Shakespeare", year: 1611}); 
 
\t \t 
 
\t \t console.log(underscore) 
 
\t \t console.timeEnd("myCode1"); 
 
\t }

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

<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'>

來源

2016-06-23 Karthikeyan sundaramoorthi

爲什麼你有一個期望，它會保持不變？電腦不穩定，時間總是會有所不同，至少有一點點。 –

如果它變得至少有點它的好，但有時它會給出1.565ms，有時.056毫秒..這不是一個微小的差異正確 –

到由於正被你的CPU進行其他工作執行代碼會有所不同的時間。由於計算機上運行的其他進程，中斷不斷髮生。您的Web應用程序只是許多需要一定CPU時間的應用程序之一。還有一些因素，例如CPU針對頻繁請求的數據執行的高速緩存以及操作系統高速緩存。

來源

2016-06-23 10:47:04

我滿意你的答案，但你能解釋爲什麼下劃線需要比正常執行更多的時間，並在控制檯窗口中打印結果時，條件反轉 –

@Karthikeyansundaramoorthi下劃線'_map'函數符合函數式編程原則，因爲它不會對傳入的數組產生任何副作用，而是將轉換函數應用於每個函數元素並返回一個新的數組。產生這種行爲的底層代碼更復雜，涉及更多的內存和處理。您可以使用'_each'來獲得更快的性能，但這會產生副作用。 –

謝謝你吉迪恩 –

爲什麼執行相同的javascript代碼所花費的時間變化

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