Summary of common Number objects in JavaScript

1. Number object

Number object is a packaging object of original numerical value.

Number is created using new Number().

2. Number syntax

var num = new Number(value);

Note: If a parameter value cannot be converted to a number, NaN (non-numeric value) will be returned.

3. Number object method

4. Number object instance

1.

• Definition and usage of

The isFinite() function is used to detect whether the specified parameter is infinity.

Tip: If number is NaN (not a number), or a positive or negative infinity number, false is returned.

Number.isFinite() is different from the global isFinite() function. The global isFinite() will first convert the detection value into Number and then detect it.

Number.isFinite() does not convert the detected value into a Number object, and returns false if the detected value is not of type Number.

Number.isFinite(123) //true
Number.isFinite(-1.23) //true
Number.isFinite(5-2) //true
Number.isFinite(0) //true
Number.isFinite('123') //false
Number.isFinite('Hello') //false
Number.isFinite('2005/12/12') //false
Number.isFinite(Infinity) //false
Number.isFinite(-Infinity) //false
Number.isFinite(0 / 0) //false

2. Number.isInteger()

• definition and usage

isInteger() function is used to detect whether the specified parameter is an integer. If it is an integer, it returns true, otherwise it returns false.

Number.isInteger(0); // true
Number.isInteger(1); // true
Number.isInteger(-100000); // true

Number.isInteger(0.1); // false
Number.isInteger(Math.PI); // false

Number.isInteger(Infinity); // false
Number.isInteger(-Infinity); // false
Number.isInteger("10"); // false
Number.isInteger(true); // false
Number.isInteger(false); // false
Number.isInteger([1]); // false

3. Number.isNaN()

• definition and usage

NaN is the abbreviation of "Not-a-Number", which is literally translated as not a number .

In JavaScript, NaN is an illegal number.

The Number.isNaN() method is used to determine whether the passed value is NaN, and checks whether its type is Number. If the value is NaN and the type is Number, it returns true, otherwise it returns false.

In JavaScript, the most special thing about NaN is that we cannot use the equality operators == and === to determine whether a value is NaN, because both NaN == NaN and NaN === NaN will return false. Therefore, there must be a way to determine whether the value is NaN.

Compared with the global function isNaN(), Number.isNaN() does not convert the parameter into a number by itself. It will return true only when the parameter is a number with a value of NaN.

Number.isNaN(NaN); // true
Number.isNaN(Number.NaN); // true
Number.isNaN(0 / 0) // true

// The following will return true if the global isNaN() is used.
Number.isNaN("NaN"); // false, the string "NaN" will not be implicitly converted to the number NaN.
Number.isNaN(undefined); // false
Number.isNaN({}); // false
Number.isNaN("blabla"); // false

//The following all return false
Number.isNaN(true);
Number.isNaN(null);
Number.isNaN(37);
Number.isNaN("37");
Number.isNaN("37.37");
Number.isNaN("");
Number.isNaN(" ");

4. Number.toFixed()

• definition and usage

The toFixed() method can round Number to a number with specified decimal places.

//Convert the number to a string, and the result will have the specified number of digits after the decimal point:

var num = 5.56789;
var n=num.toFixed(2);

//Output results:

5.57

5. Number.toPrecision(x)

• definition and usage

The toPrecision() method returns a numerical string of specified length.

The toPrecision() method returns a string representation of this numeric object with the specified precision, rounded to the number of display digits specified by the precision parameter.

// Format the number to the specified length:

var num = new Number(13.3714);
var n=num.toPrecision(2);

//Output result:

13

6. Number.toString()

• definition and usage

String representation of numbers. For example, when radix is ​​2, the NumberObject is converted to a string representing a binary value.

7. Number.valueOf()

• definition and usage

The valueOf() method can return a number as a string.