Pay attention to details in hexadecimal conversion of javascript parseInt() function_javascript skills

parseInt(string, radix) has 2 parameters. The first string is the value passed in, and the second radix is ​​the base of the passed value. The parameter radix can be ignored. The default is 10. Numbers in various bases are converted to Decimal integer (rounded down if not an integer).

The value range of radix is ​​2~36. If radix is ​​1 or radix>36, the conversion result will be NaN. If radix is ​​0 or other values ​​will be ignored, radix defaults to 10.

This function requires that the first parameter is a string. If it is not a string, it will be converted into a string. Moreover, before conversion, the left side of the string parameter conforms to the character set used by the base number. Characters are truncated for base number conversion.
Spaces at the beginning and end of string parameters will be ignored.

parseInt(param,radix) is equivalent to parseInt(String(param).trim(),radix)
For example, parseInt(010) // 8, the processing process is

Copy code The code is as follows:

010 --> 8 //Start with 0, octal number
8 -- > '8'
parseInt('8') //Ignore radix, the first parameter passed in is recognized as a decimal number

Copy code The code is as follows:

parseInt(0x10) // parseInt(16) gets decimal 16
parseInt(010,16) / / parseInt('8',16), get 8
parseInt(010,7) // parseInt('8',7), 8 exceeds the range of characters used in hexadecimal numbers and is discarded, and the conversion result is NaN
parseInt(0x10,8) // parseInt('16',8) gets 14
parseInt(0x13,8) // parseInt('19',8) character 9 exceeds the octal number used The range of characters is discarded and the conversion result is 1

If the first parameter is passed directly into the string and radix is ​​ignored, then:
The string starts with 0 and is recognized as octal by default ( IE 9 recognizes it as decimal, IE 6-8 recognizes it as octal)
The string starts with 0x and is recognized as hexadecimal by default
Otherwise, it is recognized as decimal

Copy code The code is as follows:

parseInt('010') //8,ie9 gets 10
parseInt(' 018') //1,ie9 gets 18
parseInt('017') //15, ,ie9 gets 15
parseInt('010',8) //Directly recognized as octal, the conversion result is 8
parseInt('010',7) //Directly recognized as hexadecimal, the conversion result is 7
parseInt('010',16) //Directly recognized as hexadecimal, the conversion result is 16
parseInt ('0x10') //16
parseInt('0x1g') //1
parseInt('0x1f') //31
parseInt('0x10',8) //Directly recognized as 8-digit system, the character The expression format of a hexadecimal number is correctly recognized as a hexadecimal number. The conversion result is the same as parseInt('10',16), which is 16
parseInt('0x10',17) // Recognized as a hexadecimal number, the character x Beyond the range of characters used in hexadecimal numbers, the conversion result is 0
parseInt(true) //NaN, pay attention to the usage of Boolean type in the Number function, Number(true) //1


Require special attention

1/0 // Infinity
Infinity.toString() // 'Infinity'
So here comes the trick:

Copy code The code is as follows:

parseInt(1/0,18) // NaN

parseInt(1/0,19) // 18


Because the character i is in the character set used for hexadecimal numbers, the character n and the following characters are discarded

parseInt(1/0,19) is actually parseInt('i', 19)
In addition, there is

Copy code The code is as follows:

parseInt(NaN, 36) // 30191

Because the character n is equivalent to decimal 23 in hexadecimal system, and a is equivalent to decimal 10, so there is

23*36*36 10*36 23 = 30191
parseInt(1/0,36) // 1461559270678, actually parseInt('Infinity',36)
parseFloat has no hexadecimal parameters and can only handle decimal numbers.
parseFloat.length //1