js implements the addition of two values ​​and alerts it accurately to the specified position_javascript skills

For example: Number(4.2) Number(9.2)
The sum of these two values ​​​​alerts equal to 13.3999999999999998. Why?

For example: Number(2.2) Number(9.7)
alert equals 11.899999999999998

But like this Number(2.3) Number(9.9)
alert equals 12.2. This value is what I want.

Why do some values ​​have so many decimal places when they add up, while others don’t?

Copy code The code is as follows:

< ;/head>

<script> <br><br>var a=4.2; <br>var b=9.2; <br><br>alert(Number((a b) .toFixed(2))); <br></script>