What does double mean in javascript

double means "double-precision floating point number", which uses 64 bits (8 bytes) to store a floating point number. It is a reserved word of JavaScript. Double (double-precision floating-point number) can represent 15 or 16 significant decimal digits, and the absolute value range of the number it can represent is approximately "-1.79E 308" to "1.79E 308"; double-precision floating-point number has up to 15 or 16 significant decimal digits.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

double means "double-precision floating point number" and is a reserved word in JavaScript.

Reserved words are a set of names (or commands) prepared for use within the JavaScript language. These names currently have no specific purpose and are reserved for JavaScript upgrades. Users are advised not to use them. Specific instructions are shown in the table.

##boolean enum implements package super byte export import private synchronizedchar extends int protected throwsclass final interface public transient##const Double precision floating point number (double) is a data type used by computers, using 64 bits (8 bytes) to store a floating point number. It can represent 15 or 16 significant decimal digits, and the absolute value range of the numbers it can represent is approximately: -1.79E 308 ~ 1.79E 308.

JavaScript reserved words

abstract	double	goto	native	static
float	long	short	volatile

Double precision floating point number (Double) is used to represent real numbers with decimal parts. It is generally used to define variables in computer programming. It occupies 8 bytes of storage space and its value range is -1.7E -308～1.7E 308, a double-precision floating point number has at most 15 or 16 significant decimal digits.

Double-precision binary decimal, using 64 bits to store.

1 digit11 digit52 digitS ​​(sign bit), numbered 63E (expanded code bit), numbered 62 ~52M (decimal places), number 51 ~ 00 means positive, 1 means negative1～2046AnyThe binary representation range using the reduction number specified by IEEE754 is (* represents 0 or 1):

minimum value of the reduction number*000 0000 00010000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000Maximum reduction number*

The differences between single-precision floating-point numbers (float) and double-precision floating-point numbers (double) are as follows:

(1) The number of bytes occupied in memory is different

Single-precision floating-point numbers occupy 4 bytes in the machine

Double-precision floating-point numbers occupy 8 bytes in the machine

(2) The number of valid digits is different

Single-precision floating-point number has 7 significant digits

Double-precision floating-point number has 16 significant digits

(3)The range of numbers that can be represented is different

Single-precision floating point The representation range: -3.40E 38 ~ 3.40E 38

The representation range of double precision floating point: -1.79E 308 ~ 1.79E 308

(4) The processing speed in the program is different

Generally speaking, the CPU processes single-precision floating-point numbers faster than double-precision floating-point numbers.

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	##111 1111 1110	1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111

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