Analysis and Solution of JavaScript floating point operation

Analysis

Javascript has only one numeric typeNumberAnd all numbers in JavaScript are represented in IEEE-754 standard format. The precision of floating point numbers is not unique to Javascript, because some decimals represent infinite digits in binary format:

 
Decimal binary 0.1 0.0001 1001 1001 1001... 0.2 0.0011 0011 0011 0011... 0.3 0.0100 1100 1100 1100... 0.4 0.0110 0110 0110 0110... 0.5 0.10.6 0.1001 1001 1001 1001...
 

So for example1.1, ItsProgramIn fact, it cannot really represent '1. 1', but can only be accurate to a certain extent. This is an unavoidable loss of precision:

 
1.09999999999999999
 

The problem in Javascript is more complicated. Here we only give some test data in chrome:

 
Input and Output 1.0-0.9 = 0.1 false1.0-0.8 = 0.2 false1.0-0.7 = 0.3 false1.0-0.6 = 0.4 true1.0-0.5 = 0.5 true1.0-0.4 = 0.6 true1.0- 0.3 = 0.7 true1.0-0.2 = 0.8 true1.0-0.1 = 0.9 true
 

Solution

So how can we avoid this type1.0-0.9! = 0.1What happens to non-bug issues? The following provides a more widely used solution. The accuracy of the computing result is reduced before the floating point calculation result is judged, because the accuracy is automatically rounded down:

 
(1.0-0.9 ). tofixed (digits) // The tofixed () precision parameter must be between 0 and 20, and the returned data type is stringparsefloat (1.0-0.9 ). tofixed (10) = 0.1 // The result is trueparsefloat (1.0-0.8 ). tofixed (10) = 0.2 // The result is trueparsefloat (1.0-0.7 ). tofixed (10) = 0.3 // The result is trueparsefloat (11.0-11.8 ). tofixed (10) ===- 0.8 // The result is true.
 

Method Extraction

  // use the isequal tool to determine whether the values are equal. Function isequal (number1, number2, digits) {digits = undefined? 10: digits; // The default precision is 10 return number1.tofixed (digits) === number2.tofixed (digits);} isequal (1.0-0.7, 0.3 ); // return true // native extension mode, prefer the object-oriented style number. prototype. isequal = function (number, digits) {digits = undefined? 10: digits; // The default precision is 10 return this. tofixed (digits) === number. tofixed (digits);} (1.0-0.7 ). isequal (0.3); // return true  
  
 reprint: http://madscript.com/javascript/javscript-float-number-compute-problem/