How to convert string into number in js? Summary of 5 ways to use js to convert strings into numbers

There are many ways to convert strings into numbers in js, but which method is the most appropriate? Here I will introduce five methods of converting strings into numbers, and analyze each method.

parseInt(num); // Default mode (no base)
parseInt(num, 10); // Pass in base (tens)
parseFloat(num) // Floating point number
Number(num); // Number constructor
~~num // Bitwise notation
num / 1 // Divide a number
num * 1 // Multiply a number
num - 0 // Subtract 0
num // Unary operator" "

Usage of parseInt in js:

According to the benchmark test of JsPerf.com, the maximum Most browsers respond best to parseInt. Although it is the fastest way, using preseInt will encounter some common pitfalls:

parseInt('08') // returns 0 部分老浏览器.
parseInt('44.jpg') // returns 44

parseInt: When no base is passed in, the default is the base passed in is 10 parseInt(num, 10), if you If you don’t know the type of num attribute, don’t use parseInt to convert string to number.

Usage of parseFloat in js:

If you don’t parse hexadecimal numbers, this is a very good choice. For example:

parseInt(-0xFF) // returns -255
parseInt("-0xFF") // returns -255
parseFloat(-0xFF) // returns -255
parseFloat("-0xFF") // returns 0

Note: Negative hexadecimal digits in strings are a special case, and if you parse them with parseFloat, the result will be incorrect. To avoid NaN situations in your program, you should check the converted value.

parseFloat('44.jpg') // return 44

parseFloat: Be careful when converting hexadecimal numbers. If you don't know the type of object you want to convert, don't use parseFloat.

Bitwise not in js:

can convert a string into an integer, but it is not a floating point number. If it is a string conversion, it will return 0;

~~1.23 // returns 1
~~"1.23" // returns 1
~~"23" // returns 23
~~"Hello world" // returns 0

What is the principle? By flipping) each bit, also known as the A1 complement of the number. You can use it, but note that it can only be used to store integers. So generally don't use it unless you can be sure that the number is between 32-bit integers (because of the specification of calling ToInt32).

Bitwise NOT: Use this to ensure there are no characters in the input, only for integers.

Usage of Number in js:

Number has the same problem as the conversion method mentioned above. When parsing, it tries to find out the number you gave it:

Number("023") // returns 23
Number(023) // returns 19

Note: 023 is actually an octal number, and no matter what you do, it returns 19; the same is true for hexadecimal numbers without single or double quotes.

Number is also one of the slowest in JsPerf.

Number: Rarely use it.

Usage of unary operator in js:

"1.23" * 1 // returns 1.23
"0xFF" - 0 // returns 255
"0xFF.jpg" / 1 // returns NaN
+"023" // returns 23

The unary operator is different from other parsing methods. If it is a NaN value, then the returned value is also NaN. This is my favorite way to convert numeric values, because I don't think any object with characters should be treated as 0 or "guessed" based on how many bits it has. I basically use the operator because it's less confusing this way. While -0 is fine to use, it doesn't quite convey the intent of converting to a number.

Summary of the way strings are converted to numbers:

When a negative hexadecimal number string is converted to a number. Any that should be converted to a String first (e.g. via "" ) and then parsed to a number using unary operators or parseInt with radix. But when the result is not a NaN value, it is more appropriate to use parseFloat.

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