Why jQuery's Each cycle performance is much slower than JS's native for cycle performance

2021-07-01 06:39:45
OfStack

In fact, looking at the source code of jQuery, we find that the code of each is very simple, but why is the performance 10 times different from that of the native for loop?

Core code of each for jQuery


for (; i < length; i++) { 
value = callback.call(obj[i], i, obj[i]); 
if (value === false) { 
break; 
} 
}

It looks simple, but why is it so slow?

Write the test code as follows:


var length=300000; 
function GetArr() { 
var t = []; 
for (var i = 0; i < length; i++) { 
t[i] = i; 
} 
return t; 
} 
function each1(obj, callback) { 
var i = 0; 
var length = obj.length 
for (; i < length; i++) { 
value = callback(i, obj[i]); 
/* if ( value === false ) { Remove the judgment  
break; 
}*/ 
} 
} 
function each2(obj, callback) { 
var i = 0; 
var length = obj.length 
for (; i < length; i++) { 
value = callback(i, obj[i]);/* Remove call*/ 
if (value === false) { 
break; 
} 
} 
} 
function each3(obj, callback) { 
var i = 0; 
var length = obj.length 
for (; i < length; i++) { 
value = callback.call(obj[i], i, obj[i]);/* Written by oneself call*/ 
if (value === false) { 
break; 
} 
} 
} 
function Test1() { 
var t = GetArr(); 
var date1 = new Date().getTime(); 
var lengtharr = t.length; 
var total = 0; 
each1(t, function (i, n) { 
total += n; 
}); 
var date12 = new Date().getTime(); 
console.log("1Test" + ((date12 - date1))); 
} 
function Test2() { 
var t = GetArr(); 
var date1 = new Date().getTime(); 
var total = 0; 
each2(t, function (i, n) { 
total += n; 
}); 
var date12 = new Date().getTime(); 
console.log("2Test" + ((date12 - date1))); 
} 
function Test3() { 
var t = GetArr(); 
var date1 = new Date().getTime(); 
var total = 0; 
each3(t, function (i, n) { 
total += n; 
}); 
var date12 = new Date().getTime(); 
console.log("3Test" + ((date12 - date1))); 
} 
function Test4() { 
var t = GetArr(); 
var date1 = new Date().getTime(); 
var total = 0; 
$.each(t, function (i, n) { 
total += n; 
}); 
var date12 = new Date().getTime(); 
console.log("4Test" + ((date12 - date1))); 
}

Run the test, It is found that the difference between the first and the second is not very big. This shows that the performance difference caused by break judgment is very small, but the second, third and fourth deviations are more than doubled, and the only difference between the second and third is that call is called. It seems that call will cause performance loss, because call will switch contexts. Of course, there are other reasons why each of jQuery is slow, and it also calls other methods in the loop. call is only one reason.

Therefore, it can be said that call and apply are the methods of comparing performance consumption in js, and it is recommended to use less when the performance requirements are strict.

Let's look at the performance comparison of each and js native for cycles of jquery through 1 code


<html xmlns="http://www.w3.org/1999/xhtml"> 
<head runat="server"> 
<title>for And each Performance comparison </title> 
<script src="../Cks/jquery-1.7.1.min.js" type="text/javascript"></script> 
<script type="text/javascript" language="javascript"> 
function getSelectLength() { 
var time1 = new Date().getTime(); 
var len = $("#select_test").find("option").length; 
var selectObj = $("#select_test"); 
for (var i = 0; i < len; i++) { 
if (selectObj.get(0).options[i].text == "111111") { 
selectObj.get(0).options[i].selected = true; 
break; 
} 
} 
var time2 = new Date().getTime(); 
alert("for Loop execution time: " + (time2 - time1)); 
time1 = new Date().getTime(); 
$("#select_test").find("option").each(function () { 
if ($(this).text() == "111111") { 
$(this)[0].selected = true; 
} 
}); 
time2 = new Date().getTime(); 
alert("each Loop execution time: " + (time2 - time1)); 
} 
</script> 
</head> 
<body> 
<form id="form1" runat="server"> 
<div><select id="select_test"> 
<option value='1'>111111</option> 
<option value='2'>222222</option> 
<option value='3'>333333</option> 
<option value='4'>444444</option> 
<option value='5'>5</option> 
<option value='6'>6</option> 
<option value='7'>7</option> 
<option value='8'>8</option> 
<option value='9'>9</option> 
<option value='10'>10</option> 
<option value='11'>11</option> 
<option value='12'>12</option> 
<option value='13'>13</option> 
<option value='14'>14</option> 
<option value='15'>15</option> 
<option value='16'>16</option> 
<option value='17'>17</option> 
<option value='18'>18</option> 
<option value='19'>19</option> 
<option value='20'>20</option> 
</select><input type="button" value=" Start comparing " onclick="getSelectLength();" /></div> 
<div> 
</form> 
</body> 
</html>

Input in and out:

for loop execution time: 1
each loop execution time: 3

The two results directly illustrate the problem.