js rounding

JS rounding methods: 1. tofixed method, which can round Number to a number with specified decimal places; 2. round() method, which can round a number to the nearest integer.

1. tofixed method

toFixed() method can round Number to a number with specified decimal places. For example, if the data Num is kept to 2 decimal places, it is expressed as: toFixed(Num); however, the rounding rules are different from those in mathematics. The banker's rounding rule is used. Banker's rounding: the so-called banker's rounding method , its essence is a method of rounding up to five to get even (also known as rounding up to five and leaving even). The specific rules are as follows:

To put it simply: consider rounding up to five. If the number after five is not zero, add one. If the number after five is zero, look at the odd or even number. If the number before five is even, it should be discarded. If the number before five is odd, it should be discarded. Further.

Obviously this rule does not conform to the way we usually deal with data. In order to solve this problem, you can customize the implementation using the Math.round method to specify how many bits of data to retain for processing.

2, round method

round() method can round a number to the nearest integer. For example: Math.round(x) takes x to the nearest integer. The rounding method is used in the rounding method, which conforms to the rules of rounding in mathematics. The processing of decimals is not so convenient, but it can be customized according to different requirements.

For example: to process X with two decimal places, you can use Math.round(X * 100) / 100 for processing.

Other content:

In JavaScript, the scenarios for rounding values ​​are as follows:

Round up: ceil round down: floor rounding: round fixed precision: toFixed fixed length: toPrecision rounding: parseInt, bit operation

This article will briefly explain and summarize these 6 APIs.

1. Round up: ceil

ceil means `ceiling`, which means the integer above a value and closest to the number. ceil is a static method of the Math object and needs to pass a parameter. Its calling method is as follows:

Math.ceil(12.34); //13Math.ceil(12.68); //13

2. Round down: floor

floor means `floor`, which means the nearest integer under a value. floor is a static method of the Math object and needs to pass a parameter. The calling method is as follows:

Math.floor(12.34); // 12Math.floor(12.68); // 12

3. Rounding: The function of round

round is to round a floating point number and retain the integer digits. round is also a static method of the Math object and also needs to pass a parameter. Its calling method is as follows:

Math.round(12.34); // 12Math.round(12.54); // 13

4. Fixed precision: toFixed

toFixed is different from the above three methods. It is a method implemented on the Number prototype. Its function is to round a floating point number and retain fixed decimal places. toFixed needs to pass a parameter, and its calling method is as follows:

100.456001.toFixed(2); // 100.46100.456001.toFixed(3); // 100.456

5, fixed Length: toPrecision

toPrecison is also a method implemented on the Number prototype to process floating-point numbers. The difference from toFixed is that it rounds a floating-point number and retains a fixed length of significant digits, including the integer part.

99.456001.toPrecision(5); // 99.456100.456001.toPrecision(5); // 100.46

6. Rounding: parseInt

parseInt Yes A method on the global object window, its function is to round a convertible value, which is divided into the following two situations:

1. Convert the string value into a Number integer, and round each value in the string Characters are converted until an unconvertible character (including a decimal point) is encountered.

2. Round floating point type values, ignore the decimal part, and do not round

// String value parseInt('100'); // 100parseInt('100axt') ; // 100parseInt('100xh20'); // 100parseInt('100.78'); // 123// Number type parseInt(100.12); // 100parseInt(100.78); // 100

7. Rounding: Bit operations

| 0: Perform a bitwise OR operation with 0, the original value remains unchanged~~: The original value obtained by two bitwise NOT operations is also the original value>> 0: Right shift 0 bits<< 0: Left shift 0 bits>>> 0: Unsigned right shift 0 bits

These bit operators will show some common characteristics when implementing rounding operations. :

For the Number type, applying bit operations directly will result in almost the same result as parseInt; for other types, it will be converted to a numeric value internally through Number(), and then bit operations will be applied. When bit operations are applied to the special NaN and Infinity values, both values ​​are treated as 0.

For Number type, bit operations are applied directly.

~~ 100.12; // 100100.78 | 0; // 100100.45 >> 0; // 100100.50 << 0; // 100100.96 >>> 0; // 100

For other types, first use Number() to convert to numeric type, and then perform bit operations.

~~ '100.12' // 100, Number('100.12') == 100.12'100.50' >> 0; // 100, Number('100.50') == 100.50'100.96' < ;< 0; // 100, Number('100.96') == 100.96~~ 'abc' // 0, Number('abc') == NaN'12abc' >> 0; // 0, Number ('12abc') == NaNundefined | 0 ; // 0, Number(undefined) == NaN~~null; // 0 , Number(null) == 0true >> 0; // 1 , Number(true ) == 1false >> 0; //0 , Number(false) == 0[] << 0; // 0 , Number([]) == 0~~NaN; // 0 Infinity > ;>> 0; // 0

Bit operations operate at the most basic level, that is, operating on values ​​based on the bits in memory that represent the value.

The reason why bit operations can be rounded is:

The values ​​in ECMAScript are stored as 64-bit double-precision floating point numbers, but bit operations can only be applied to integers, so the 64-bit floating point numbers must be converted first. The point number is converted into a 32-bit integer, and then bit operations are performed, and finally the calculation result is converted into a 64-bit floating point number for storage.

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