JavaScript で浮動小数点数を整数に変換するにはどうすればよいですか?

Converting Float Numbers to Whole Numbers in JavaScript

Converting float numbers to whole numbers is a common task in JavaScript. There are two primary methods to accomplish this: truncation and rounding.

Truncation with Math.floor()

Truncation involves removing the decimal portion of a number, resulting in the nearest integer towards negative infinity. This is achieved using the Math.floor() function:

var intvalue = Math.floor(floatvalue);

Rounding with Math.ceil() and Math.round()

Rounding can be performed in two ways:

• Math.ceil(): Rounds the number up to the nearest integer towards positive infinity.
• Math.round(): Similar to Math.ceil(), but rounds to the nearest integer, even if it's towards negative infinity when the fractional part is exactly 0.5.

The code below demonstrates these methods:

var intvalue = Math.ceil(floatvalue); 
var intvalue = Math.round(floatvalue);

Additional Considerations

• Math.trunc(): Available in ECMAScript 6, this function specifically truncates the number without rounding.
• Other Methods: Bit manipulation operators like ~, >>, and >>> can also be used to convert floats to integers, although they may not be as efficient.

Examples

The following table illustrates the different conversion methods with various input values:

Value	Math.floor()	Math.ceil()	Math.round()
Positive (Less than 3.5)	Truncated	Rounded up	Rounded up
Positive (Greater than or equal to 3.5)	Truncated	Rounded up	Rounded up
Negative (Greater than -3.5)	Rounded up	Truncated	Truncated
Negative (Less than or equal to -3.5)	Rounded up	Truncated	Rounded down

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