ECMA-262 Core: JavaScript Number Data Type



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Introduction And Review

The ECMA-262 standard defines the term Number Type as: a set of values representing numbers. In ECMAScript, the set of values represent the double-precision 64-bit format IEEE 754 values.

The Number data type is one of five ECMAScript primitive types. The other four are: String, Boolean, Null and Undefined. All primitive types have a definite (fixed) size except for the String type.

The Number type is distinguished from other types using a dynamic or weak typing method. The dynamic method involves interrogating the literal token for a range of values to determine whether it is a integer or floating point number.

Number Type



Special Situations Using Numbers in JavaScript
Statement   Result   Comment
1st operand operator 2nd operand
0 divide 0 NaN Divide zero by zero will result in NaN.
1 divide 0 Infinity Divide a positive number by zero will result in Infinity.
-1 divide 0 -Infinity Divide a negative number by zero will result in negative Infinity.
-Infinity add Infinity NaN Add Infinity to -Infinity will result in NaN.
Infinity == Infinity true All Infinity values compare equal.
-Infinity == -Infinity true All -Infinity values compare equal.
numvar = Number(string) type change When a string contains all numbers, you can convert the type to a number by using the Number constructor as a function.
numvar = string - 0 type change When a string contains all numbers, you can convert the type to a number by performing a numeric operation on it.
numvar = Number(false) 0 Here is some more type changes where non-numeric values ( valid literals for other types) are cast as numeric types.
numvar = Number(true) 1
numvar = Number(null) 0
numvar = Number("43") 43
numvar = Number("4.3") 4.3
numvar = Number(undefined) NaN More attempts at type casting; these two are errors. "Undefined" is not a valid literal and the string can not be converted into a legitimate float.
numvar = Number("4.3.2") NaN
biggest = Number.MAX_VALUE MAX_VALUE Assign the maximum allowed value to a variable.
toobig = Number.MAX_VALUE + 1 Infinity Assigned a value too big for 64-bits. Any number larger than the maximum is POSITIVE_INFINITY.
toosmall = Number.MIN_VALUE - 1 -Infinity Assigned a value too small for 64-bit limit;
-Infinity and Number.NEGATIVE_INFINITY are the same value.
hexnum = 0xf 15 Some hexadecimal examples. Hex digits may be either lower or uppercase. Remember:
0-9 equates to 0-9 decimal
A equates to 10 decimal
B equates to 11 decimal
C equates to 12 decimal
D equates to 13 decimal
E equates to 14 decimal
F equates to 15 decimal
hexnum = 0x0 0
hexnum = 0xFF 255
hexnum = 0x100 256
hexnum = 0xfff 4,095
hexnum = 0x1000 4,096
hexnum = 0xFFFF 65,535
hexnum = 0x10000 65,536
hexnum = 0xFFFFF 1,048,575
hexnum = 0xABCDEF 11,259,375
afloat = 3.98E4 39800 E-notation for a float;
3.98 X 10 X 10 X 10 X 10
5.3 + 3.7 9 Two floats that make a whole number will give an integer as the result.


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