What is the method to convert string to number?

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JavaScript is a magical language, string There are 5 methods of converting numbers, each with its own pitfalls! Next, through this article, I will introduce to you the 5 methods of converting JavaScript strings to numbers and their pitfalls. Friends who are interested should take a look together

Which one to choose? What about one kind? When to choose it? Why choose this kind of it? We go through them one by one and break down the common pitfalls of each approach.

parseInt

According to JsPerf.com’s benchmarks, most browsers respond best to parseInt. Although it is the fastest way, you will encounter some common pitfalls when using preseInt:

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.

parseFloat

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 a string are a special case, and if you parse 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

You 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.

Number

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: Hardly use it.

Unary cloud operator

"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 to convert strings to numbers

When converting negative hexadecimal number strings to numbers. 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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