x
.
toPrecision
(
2
);
// "1.0e+3"
x
.
toPrecision
(
1
);
// "1e+3"
x
=
15.335
;
x
.
toPrecision
(
6
);
// "15.3350"
x
.
toPrecision
(
5
);
// "15.335"
x
.
toPrecision
(
4
);
// "15.34"
x
.
toPrecision
(
3
);
// "15.3"
x
.
toPrecision
(
2
);
// "15"
x
.
toPrecision
(
1
);
// "2e+1"
Output is rounded, and will always have the specified number of digits of precision. If
necessary, output will be in exponential notation.
Different Bases
If you want to display numbers in a different base (such as binary, octal, or hexadeci‐
mal),
Number.prototype.toString
takes an argument specifying the base (in the
range 2 to 36):
const
x
=
12
;
x
.
toString
();
// "12" (base 10)
x
.
toString
(
10
);
// "12" (base 10)
x
.
toString
(
16
);
// "c" (hexadecimal)
x
.
toString
(
8
);
// "14" (octal)
x
.
toString
(
2
);
// "1100" (binary)
Advanced Number Formatting
If you’re displaying a lot of numbers in your application, your needs may quickly sur‐
pass what the built-in JavaScript methods provide. Common needs are:
• Thousands separators
• Displaying negative numbers differently (for example, with parentheses)
• Engineering notation (similar to exponential notation)
• SI prefixes (milli-, micro-, kilo-, mega-, etc.)
Providing this functionality can be educational if you’re looking for a reader’s exer‐
cise. If you’re not, I recommend the
functionality and more.
Constants
The usual important constants are available as properties of the
Math
object:
// fundamental constants
Math
.
E
// the root of the natural logarithm: ~2.718
Math
.
PI
// the ratio of a circle's circumference to its diameter: ~3.142
Constants | 231
