Number Precision in JavaScript

Following methods is referenced from developer.mozilla.org.

Number.prototype.toPrecision()

The toPrecision() method returns a string representing the Number object to the specified precision.

Example:

var test = 1.999
test.toPrecision() //1.999

var test2 = 1.511
test2.toPrecision(1) //2
test2.toPrecision(2) //1.5

var test3 = 1.001
test3.toPrecision(1) //1
test3.toPrecision(2) //1.0

var test4 = 0.999
test4.toPrecision(1) //1
test4.toPrecision(2) //1.0

Number.prototype.toFixed()

The toFixed(parameter) method formats a number using fixed-point notation.

The parameter may be a value between 0 and 20, inclusive. If no parameter, it is treated as 0.

This function returns a string representation of the number that does not use exponential notation and has exactly digits digits after the decimal place. The number is rounded if necessary, and the fractional part is padded with zeros if necessary so that it has the specified length.

Example:

test = 2.059
test.toFixed() //2
test.toFixed(1) //2.1
test.toFixed(2) //2.06

test2 = 2e+10
test2.toFixed(1) //20000000000.0

toPrecision() is to count the total length. toFixed() is to count length after decimal point.

Number.prototype.toExponential()

The toExponential(parameter) method returns a string representing the Number object in exponential notation.

The parameter specifying the number of digits after the decimal point.

If you use the `toExponential()`` method for a numeric literal and the numeric literal has no exponent and no decimal point, leave a space before the dot that precedes the method call to prevent the dot from being interpreted as a decimal point.

Example:

test = 2.019
test.toExponential() //'2.019e+0'
test.toExponential(1) //'2.0e+0'
test.toExponential(2) //'2.02e+0'