Rounding In Javascript Tofixed() Method

I have known that the toFixed() method in javascript converts a number into a string, keeping a specified number of decimals, just like the code shown below, which sets the number

Solution 1:

As stated in the docs, toFixed()does round when necessary. The rounding behavior is to round in the range -.5 < x <= +.5 of the digit.

The strange behavior you're observing is consistent with the note in the docs linked above:

Floating point numbers cannot represent all decimals precisely in binary which can lead to unexpected results such as 0.1 + 0.2 === 0.3 returning false .

In other words, this is a classic case of floating point precision loss - a problem you'll encounter in virtually any language. If you observe the full outputs of a and b you'll see that a == 0.075 and b == 0.07500000000000001 due to floating point precision - and thus given these values it is consistent with the defined rounding behavior to round a to .07 and b to .08.

Solution 2:

The problem you are encountering is not specific to JavaScript, it is common to computing in general.

Both these arithmetic calculations have the same result – 0.075:

• 0.25 * 0.3 = 0.075
• 0.025 * 3 = 0.075

This is using the decimal number system commonly used.

Computers, at their core, however, don't use the decimal system, but binary – everything is based on 0 and 1.

Because of this, they actually have a hard time getting the calculation above right. JavaScript and other programming languages have to approximate the result, giving you this:

• 0.25 * 0.3 = 0.75
• 0.025 * 3 = 0.07500000000000001

You can now see why toFixed returns different results:

• 0.75.toFixed(2) = 0.07
• 0.07500000000000001.toFixed(2) = 0.08