Share 5 ways to convert JS strings to numbers

JavaScript is a magical language. There are 5 ways to convert strings to numbers, each with its own pitfalls!

This article introduces 5 methods of converting JavaScript strings to numbers and their pitfalls. I hope it will be helpful to everyone.

There are many ways to convert String to Number, I can think of 5!

parseInt(num); // 默认方式 (没有基数)
parseInt(num, 10); // 传入基数 (十位数)
parseFloat(num); // 浮点数
Number(num); // Number 构造器
~~num; //按位非
num / 1; // 除一个数
num * 1; // 乘一个数
num -0  // 减去0
+ num; // 一元运算符 "+"

Which one to choose? 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, 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 base is 10 parseInt(num, 10), if you don’t know the type of num attribute, do not use parseInt to convert string to number.

parseFloat

This is a very good choice if you don't parse hexadecimal numbers. 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 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

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's 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 are sure that the number is between 32-bit integers (due to 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. Although the usage of -0 is also good, it does not express the original intention of converting to a number very well.

Best way to convert string to number?

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

Recommended tutorial: "JS Tutorial"

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