Example analysis of float operation precision in javascript

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Example analysis of float operation precision in javascript_javascript skills

May 16, 2016 pm 06:20 PM

float

Someone asked a js question:

Copy code The code is as follows:

 
var i = 0.07; 
var r = i*100; 
alert(r); 

Why is the result 7.0000000000000001?
After checking the information, we actually know that in JavsScript, when variables are stored There is no distinction between number and float types, but they are stored uniformly as float. JavaScript uses the 64-bit floating point format defined by the IEEE 754-2008 standard to store numbers. According to the definition of IEEE 754: http://en.wikipedia.org/wiki/IEEE_754-2008
The length of the integer corresponding to decimal64 is 10, The length of the decimal part is 16, so the default calculation result is "7.0000000000000001". If the last decimal is 0, take 1 as the valid digit flag.

Similarly, we can imagine that the result of 1/3 should be 0.3333333333333333.
So how to correct this value?
You can use the following methods:
1. parseInt

var r4=parseInt(i*100);

2. Math.round

var r2=Math.round((i*100)*1000)/1000;

Both of the above two methods can get 7
Attached is the full test code:

Copy code The code is as follows:

 
<html> 
<head> 
<title>Test script</title> 
<script language="JAVASCRIPT"> 
function init() 
{ 
var i = 0.07; 
var r = i*100; 
var r2=Math.round((i*100)*1000)/1000; 
var r3 = eval(i*100); 
var r4=parseInt(i*100) ; 
var r5=parseFloat(i*100*1.0000); 
var r6=(1/3); 
alert(r); 
alert("Math.round=" r2); 
alert("eval=" r3); 
alert("parseInt=" r4); 
alert("parseFloat=" r5); 
alert("" r6); 
} 
</script> 
</head> 
<body onload="init();"> 
</body> 
</html> 

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