Work With Numbers in JavaScript II

In JavaScript, beyond numeric data, the Number type is also used to represent special values like NaN, Infinity, or -Infinity.

Convert expressions to numbers

To convert a string or an expression into an integer or a floating point number, you can use the global built-in Number function:

Number(expression)

Note that if the value can't be converted into a valid number, the Number function will return NaN.

Example

In this example, all values will be converted to numbers:

Number(1)       // 1
Number('123')   // 123
Number(null)    // 0
Number(true)    // 1
Number(false)   // 0

However, these values will be converted to NaN:

Number('text')      // NaN
Number(undefined)   // NaN

Convert strings to integers

To convert a string to an integer, you can use the global built-in parseInt function:

parseInt(string, base?)

Where:

• string is a string starting with an integer.
• base is an optional number between 2 and 36 representing the mathematical base. Defaults to 10.

Notes:

• The parseInt function will automatically ignore whitespaces, leading zeros, and remove the decimal part.
• The parseInt function will return the NaN value if the value cannot be converted into a number.

Example

In this example, all strings will be converted to numbers:

parseInt('123')       // 123
parseInt('   123 ')   // 123
parseInt('077')       // 77
parseInt('1.9')       // 1
parseInt('0xff', 16)  // 255

However this string will be converted to NaN:

parseInt('xyz')   // NaN

Convert strings to floating point numbers

To convert a string to a floating point number, you can use the global built-in parseFloat function:

parseFloat(string)

Notes:

• The parseFloat function doesn't support non-decimal literals starting with 0x, 0b, or 0o, and will return 0.
• The parseFloat function will return the NaN value if the value cannot be converted into a number.

Example

In this example, all strings will be converted to floating point numbers:

parseFloat('123')       // 123
parseFloat('   123 ')   // 123
parseFloat('1.9')       // 1.9
parseFloat('0xff')      // 0

However this string will be converted to NaN:

parseFloat('xyz')   // NaN

Not-a-number

In JavaScript, NaN (Not-a-Number) is a special value that results from arithmetic operations or expressions that don't yield a valid number.

Example

In this example, the following expressions all evaluate to NaN:

// Dividing zero by zero
0 / 0

// Performing operations where JavaScript fails to coerce types
"text" - 2

// Performing operations involving undefined
1 + undefined

// Performing operations involving NaN
NaN + 5

Checking if a value is a number

To test whether an expression is a valid number or not, you can use the built-in global isNaN function as follows:

isNaN(expression)

Upon execution, the isNaN function first converts the expression to a number and then returns true if the resulting value is not a number, or false otherwise.

Infinity

In JavaScript, Infinity and -Infinity represent values that are beyond the largest or smallest finite number that can be represented.

Example

For example, the following expressions all evaluate to Infinity or -Infinity:

1 / 0                  // Infinity
-1 / 0                 // -Infinity
Number.MAX_VALUE * 2   // Infinity
Number("1e309")        // Infinity

Checking if a value is finite

To test whether an expression is a finite number, you can use the built-in global isFinite function.

isFinite(expression)

Upon execution, the isFinite function first tries to convert the expression to a number, and then either returns false if the conversion results in NaN, Infinity, or -Infinity, or true otherwise.

Adjusting numbers length

Adjusting the number of decimals

To trim a floating point number to a fixed number of decimals, you can use its toFixed method.

number.toFixed(digits)

Where digits is the number of decimals you want to keep.

Example

For example:

1.2345.toFixed(2)   // 1.23

Adjusting the number of digits

To trim an integer or a floating point number to a fixed number of digits, you can use its toPrecision method.

number.toPrecision(digits);

Where digits is the number of digits you want to keep.

Example

For example:

1.2345.toPrecision(2)   // 1.2

The built-in Math library

JavaScript provides a built-in Math object for more advanced mathematical operations.

Rounding numbers

To round a number to the nearest integer up, you can use the ceil static method.

Math.ceil(number)

To round a number to the nearest integer down, you can use the floor static method.

Math.floor(number)

To round a number to the nearest integer, you can use the round static method.

Math.round(number)

Example

For example:

Math.ceil(1.2)    // 2
Math.floor(1.6)   // 1
Math.round(1.2)   // 1

Generating random numbers

To generate a random number between 0 (included) and 1 (excluded), you can use the random static method.

Math.random()

Example

Let's consider this script:

function getRandomNumber(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(getRandomNumber(0, 1));
console.log(getRandomNumber(1, 10));
console.log(getRandomNumber(1, 100));

When executed, it will execute the getRandomNumber function to return integers in the range specified by the min and max values.

Which will produce this output:

1
6
82

Summary

Here's a summary of what you've learned in this lesson:

• The global Number function is used to convert expressions into numbers.
• The global parseInt function is used to convert strings to integers.
• The global parseFloat function is used to convert strings to floating point numbers.
• The NaN (Not-a-Number) is a value resulting from arithmetic operations or expressions that don't yield a valid number.
• The global isNaN function is used to check if an expression is a valid number.
• The Infinity and -Infinity represent values that are beyond the largest or smallest finite number that can be represented.
• The global isFinite function is used to check if an expression is a finite number.
• The toFixed method is used to trim a floating point number to a fixed number of decimals.
• The toPrecision method is used to trim an integer or a floating point number to a fixed number of digits.
• The Math.ceil method is used to round a number to the nearest integer up.
• The Math.floor method is used to round a number to the nearest integer down.
• The Math.round method is used to round a number to the nearest integer.
• The Math.random method is used to generate a random number between 0 (included) and 1 (excluded).