JavaScript Numbers

JavaScript has only one number type.

Whether to write a decimal point when writing a number is optional.

JavaScript Number

JavaScript numbers can be written with or without a decimal point:

Example

var x = 3.14;    // A number with a decimal point
var y = 3;       // A number without a decimal point

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Very large or very small numbers can be written in scientific notation:

Example

var x = 123e5;    // 12300000
var y = 123e-5;   // 0.00123

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JavaScript numbers are always 64-bit floating-point numbers

Unlike many other programming languages, JavaScript does not define different types of numbers, such as integers, shorts, longs, floats, etc.

JavaScript numbers are always stored as double-precision floating-point numbers, according to the international IEEE 754 standard.

This format stores numbers with 64 bits, where 0 to 51 store the number (fraction), 52 to 62 store the exponent, and 63 bits store the sign:

Value (also known as Fraction/Mantissa) Exponent Sign
52 bits(0 - 51) 11 bits (52 - 62) 1 bit (63)

Precision

Integers (not using exponent or scientific notation) are precise to 15 digits.

Example

var x = 999999999999999;   // x will be 999999999999999
var y = 9999999999999999;  // y will be 10000000000000000

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The maximum number of decimal places is 17, but floating-point arithmetic is not always 100% accurate:

Example

var x = 0.2 + 0.1;         // x will be 0.30000000000000004

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Using multiplication and division can help solve the above problem:

Example

var x = (0.2 * 10 + 0.1 * 10) / 10;       // x will be 0.3

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Adding a number and a string

Warning!!

JavaScript's addition and concatenation (concatenation) both use the + operator.

Numbers use addition. Strings use concatenation.

If you add two numbers, the result will be a number:

Example

var x = 10;
var y = 20;
var z = x + y;           // z will be 30 (a number)

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If you add two strings, the result will be a string concatenation:

Example

var x = "10";
var y = "20";
var z = x + y;           // z will be 1020 (string)

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If you add a number and a string, the result will also be a string concatenation:

Example

var x = 10;
var y = "20";
var z = x + y;           // z will be 1020 (a string)

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If you add a string and a number, the result will also be string concatenation:

Example

var x = "10";
var y = 20;
var z = x + y;           // z will be 1020 (string)

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A common mistake is to think the result should be 30:

Example

var x = 10;
var y = 20;
var z = "The result is: " + x + y;

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A common mistake is to think the result should be 102030:

Example

var x = 10;
var y = 20;
var z = "30";
var result = x + y + z;

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JavaScript compiles from left to right.

Because x and y are both numbers, 10 + 20 will be added.

Because z is a string, 30 + "30" is concatenated.

Numeric string

JavaScript strings can contain numeric content:

var x = 100;         // x is a number
var y = "100";       // y is a string

In all numeric operations, JavaScript will try to convert strings to numbers:

This example runs as follows:

var x = "100";
var y = "10";
var z = x / y;       // z will be 10

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This example will also run as follows:

var x = "100";
var y = "10";
var z = x * y;       // z will be 1000

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This example runs as follows:

var x = "100";
var y = "10";
var z = x - y;      // z will be 90

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But this example will not run as expected:

var x = "100";
var y = "10";
var z = x + y;       // z will not be 110 (but 10010)

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In the last example, JavaScript concatenated strings using the + operator.

NaN - Not a Number

NaN It is a reserved word in JavaScript, indicating that a number is not a valid number.

Trying to divide by a non-numeric string will result in NaN (Not a Number):

Example

var x = 100 / "Apple";  // x will be NaN (Not a Number)

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However, if the string contains a number, the result will be a number:

Example

var x = 100 / "10";     // x will be 10

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You can use the global JavaScript function isNaN() to determine if a value is a number:

Example

var x = 100 / "Apple";
isNaN(x);               // Returns true because x is not a number

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in mathematical operations. NaN.Be careful if you use NaNthen the result will also be NaN:

Example

var x = NaN;
var y = 5;
var z = x + y;         // z will be NaN

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The result may be a concatenation:

Example

var x = NaN;
var y = "5";
var z = x + y;         // z will be NaN5

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NaN is a number,typeof NaN returns number:

Example

typeof NaN;             // Returns "number"

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Infinity

Infinity （or -Infinity）is the value returned by JavaScript when it exceeds the maximum possible number range during calculation.

Example

var myNumber = 2;
while (myNumber != Infinity) {          // Execute until Infinity
    myNumber = myNumber * myNumber;
}

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Dividing by 0 (zero) will also generate Infinity:

Example

var x =  2 / 0;          // x will be Infinity
var y = -2 / 0;          // y will be -Infinity

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Infinity is a number:typeOf Infinity returns number.

Example

typeof Infinity;        // Returns "number"

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hexadecimal

JavaScript will interpret numbers prefixed with 0x to interpret the numerical constants as hexadecimal.

Example

var x = 0xFF;             // x will be 255.

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Never write numbers with leading zeros (like 07).

Some JavaScript versions interpret numbers with leading zeros as octal.

By default, JavaScript displays numbers as decimal numbers.

However, you can use toString() The method outputs the number in hexadecimal, octal, or binary.

Example

var myNumber = 128;
myNumber.toString(16);     // Returns 80
myNumber.toString(8);      // Returns 200
myNumber.toString(2);      // Returns 10000000

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Numbers can also be objects

JavaScript numbers are usually created through literals: var x = 123

But it can also be done through the keyword new Defined as an object: var y = new Number(123)

Example

var x = 123;
var y = new Number(123);
// typeof x returns number
// typeof y returns object

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Please do not create number objects. This will slow down the execution speed.

new The keyword complicates the code and produces some unexpected results:

When using == The numbers look equal when using the equality operator:

Example

var x = 500;             
var y = new Number(500);
// (x == y) is true because x and y have equal values

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When using === After the equality operator, the numbers that are equal become unequal because === Operators need both type and value to be equal.

Example

var x = 500;             
var y = new Number(500);
// (x === y) is false because x and y are of different types

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Even worse. Objects cannot be compared:

Example

var x = new Number(500);             
var y = new Number(500);
// (x == y) is false because objects cannot be compared

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JavaScript objects cannot be compared.