JavaScript学习-- Number数据类型

1. 整数数据类型

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var intNum = 55; //integer  

   

var octalNum1 = 070; //octal for 56  

var octalNum2 = 079; //invalid octal - interpreted as 79  

var octalNum3 = 08; //invalid octal - interpreted as 8  

   

var hexNum1 = 0xA; //hexadecimal for 10  

var hexNum2 = 0x1f; //hexedecimal for 31  

2. 浮点数数据类型

 

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var floatNum1 = 1.1;  

var floatNum2 = 0.1;  

var floatNum3 = .1; //valid, but not recommended  

   

var floatNum1 = 1.; //missing digit after decimal - interpreted as integer1  

var floatNum2 = 10.0; //whole number - interpreted as integer 10  

   

var floatNum = 3.125e7; //equal to 31250000  

3. NaN -- not a number

 

1）包含NaN值的任何运算的返回值均是NaN

 

2）NaN与任何其它数值都不相等，包括其它NaN

 

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alert(NaN == NaN); //false  

3）NaN判断：isNaN()，可对任何数据进行判断，任何不可被转换为数字的数据均返回true

 

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alert(isNaN(NaN)); //true  

alert(isNaN(10)); //false - 10 is a number  

alert(isNaN(“10”)); //false - can be converted to number 10  

alert(isNaN(“blue”)); //true - cannot be converted to a number  

alert(isNaN(true)); //false - can be converted to number 1  

当isNaN()的参数是对象时，先调用对象的valueOf()方法进行数字转换，如果无法转换为数字则继续调用对象的toString()方法进行数字转换来判断。

 

4. Number Conversions

 

1）Number()

 

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var num1 = Number(“Hello world!”); //NaN  

var num2 = Number(“”); //0  

var num3 = Number(“000011”); //11  

var num4 = Number(true); //1  

2）parseInt()

 

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var num1 = parseInt(“1234blue”); //1234  

var num2 = parseInt(“”); //NaN  

var num3 = parseInt(“0xA”); //10 - hexadecimal  

var num4 = parseInt(22.5); //22  

var num5 = parseInt(“70”); //70 - decimal  

var num6 = parseInt(“0xf”); //15 - hexadecimal  

   

var num = parseInt(“0xAF”, 16); //175  

var num1 = parseInt(”AF”, 16); //175  

var num2 = parseInt(”AF”); //NaN  

   

var num1 = parseInt(“10”, 2); //2 - parsed as binary  

var num2 = parseInt(“10”, 8); //8 - parsed as octal  

var num3 = parseInt(“10”, 10); //10 - parsed as decimal  

var num4 = parseInt(“10”, 16); //16 - parsed as hexadecimal  

3）parseFloat()

 

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var num1 = parseFloat(“1234blue”); //1234 - integer  

var num2 = parseFloat(“0xA”); //0  

var num3 = parseFloat(“22.5”); //22.5  

var num4 = parseFloat(“22.34.5”); //22.34  

var num5 = parseFloat(“0908.5”); //908.5  

var num6 = parseFloat(“3.125e7”); //31250000  

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