Strange behavior in Javascript

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1

This question is more out of curiosity, I’ve already answered the problem in my code.

I made a money mask using javascript, it was working perfectly, until I entered the value 4.9.

Debugging the code found that the problem was multiplying the value 4.9 by 100, the result of this multiplication gave:

490.00000000000006

What made my mask "bugger".

Other values like 4.8 the result is shown correctly, like:

480

Follow the code below to illustrate:

alert(4.9*100);

//Sem problemas
alert(4.8*100);

//Outro exemplo mais grave
alert(4.6*100);

My question is this, why is there this strange behavior in Javascript? I did the same multiplication using php and it worked normally.

And for those who had the same problem and just want to solve, I solved it in the following way:

var valor = 4.9;
resultado = (valor  * 100).toFixed(2);
alert(valor);

var valor = 4.6;
resultado = (valor  * 100).toFixed(2);
alert(valor);

javascript
  • 2

    Briefly, calculations with floating point numbers are not exact

  • 3

    Would that be? https://answall.com/questions/14728/realizes%C3%A7%C3%A3o-de-floating-point-in-javascript-with-precis%C3%A3o-absolute

  • 2

    this is an old known number rounding problem in javascript, has this interesting question in the OS in English: how-to-Deal-with-floating-point-number-Precision-in-javascript

1 answer

1

This has to do with the IEEE regulation for binary representation for floating point number. A good way out is also to work with integers, multiplying your coin by 100 before operating and then dividing by 100 to see with the cents after the point.

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