How to convert a string into a number in JavaScript

The main methods are: 1. parseInt() ; 2. Number() ; 3. parseFloat() ;

Let's introduce them one by one:

1.parseInt(string, radix)

• Parses a string and returns a decimal integer in the specified radix or NaN.
• The first argument is the value to be parsed. If the argument is not a number, it is converted to a number;
• The second parameter specifies the base of the parsed value.
• If the first character passed in cannot be converted to a number, parseInt returns NaN.
  

Here is a compatibility issue:

If radix is undefined , 0 , or unspecified, JavaScript assumes the following:

• If the input string begins with "0x" or "0x" (a 0 followed by a lowercase or uppercase X), radix is ​​assumed to be 16 and the rest of the string is parsed as a hexadecimal number.
  
• If the input string begins with "0" (0), radix is ​​assumed to be 8 (octal) or 10 (decimal). The exact radix chosen is implementation dependent. ECMAScript 5 clarified that 10 (decimal) should be used, but not all browsers support this yet. Therefore, when using parseInt , be sure to specify a radix.
• If the input string begins with any other value, radix is ​​10 (decimal).
  

2. Number()

Function converts the value of an object to a number

• Number() function converts the value of an object to a number.
• When a string is passed to Number() conversion function, it will try to convert it to an integer or floating point number directly. This method can only convert based on decimal. If non-numeric characters appear in the string, NaN will be returned.
  

3.parseFloat()

• The given value is parsed as a floating point number or integer. If it cannot be converted to a number, NaN is returned.
• parseFloat is a global function and does not belong to any object.
  

All can be used directly:

function circumference(r) {
  return parseFloat(r) * 2.0
}
 
console.log(circumference(3));
// Output: 6

Finally, there is a more powerful operation:

數字字符串前直接寫“+”直接轉換

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