Summary of common Number objects in JavaScript

This article brings you relevant knowledge about javascript, which mainly sorts out issues related to the Number object. The Number object is a packaging object of the original value. The Number creation method is new Number(). Let’s take a look at it together, I hope it will be helpful to everyone.

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1. Number object

Number objects are wrapper objects for primitive numbers.

Number creation method new Number().

2. Number syntax

var num = new Number(value);

Note: If a parameter value cannot Converting to a number returns NaN (not a numeric value).

3. Number object method

Method	Description
isFinite()	Detects whether the specified parameter is infinity.
isInteger()	Check whether the specified parameter is an integer.
isNaN()	Detects whether the specified parameter is NaN.
toFixed(x)	Convert the number to a string. The result has the specified number of digits after the decimal point.
toPrecision(x)	Format the number to the specified length.
toString()	Convert a number to a string, using the specified base.
valueOf()	Returns the basic numeric value of a Number object.

## 4.

Number object instance

1. Number.isFinite()

Definition and Usage

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

Tips: 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 detection value to a Number object, and returns false if the detection value is not of Number type.

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 specified parameters Whether it 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 "Not-a-Number" The abbreviation of , literally translated as

is not a number .

In JavaScript, NaN is an illegal number.

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 be returned false. Therefore, there must be a way to determine whether the value is NaN.

Compared with the global function isNaN(), Number.isNaN() will 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

// 下面这几个如果使用全局的 isNaN() 时，会返回 true。
Number.isNaN("NaN");      // false，字符串 "NaN" 不会被隐式转换成数字 NaN。
Number.isNaN(undefined);  // false
Number.isNaN({});         // false
Number.isNaN("blabla");   // false

// 下面的都返回 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

toFixed() method can round Number to Number specifying the number of decimal places.

//把数字转换为字符串，结果的小数点后有指定位数的数字：

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

//输出结果:

5.57

5. Number.toPrecision(x)

Definition and usage

toPrecision() method returns the specified length Numeric string.

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.

// 把数字格式化为指定的长度:

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

// 输出结果:

13

6. Number.toString()

Definition and usage

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

7. Number.valueOf()

Definition and usage

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

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javascript video tutorial, web front-end】

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