JavaScript is very flexible about the types of values it requires.
When JavaScript expects a boolean value, you may supply a value of any type, and JavaScript will convert it as needed.
If JavaScript wants a string, it will convert whatever value you give it to a string.
If JavaScript wants a number, it will try to convert the value you give it to a number(or to NaN if it cannot perform a meaningful conversion).
例如:
10 + " objects" // => "10 objects". Number 10 converts to a string
"7" * "4" // => 28: both strings convert to numbers
var n = 1 - "x"; // => NaN: string "x" can't convert to a number
n + " objects" // => "NaN objects": NaN converts to string "NaN"
显式转换:
显式转换最简单的方式是使用:Boolean(), Number(), String(), or Object() functions.
例如:
Number("3") // => 3
String(false) // => "false" or use false.toString()
Boolean([]) // => true
Object(3) // => new Number(3)
The toString() method defined by the Number class accepts an optional argument that specifies a radix, or base, for the conversion. If you do not specify the argument, the conversion is done in base 10. However, you can also convert numbers in other bases (between 2 and 36).
例如:
var n = 17;
binary_string = n.toString(2); // Evaluates to "10001"
octal_string = "0" + n.toString(8); // Evaluates to "021"
hex_string = "0x" + n.toString(16); // Evaluates to "0x11"
数值处理:
Number(): If you pass a string to the Number() conversion function, it attempts to parse that string as an integer or floating-point literal. That function only works for base-10 integers, and does not allow trailing characters that are not part of the literal.
parseInt():
parseFloat(): The parseInt() and parseFloat() functions (these are global functions, not methods of any class) are more flexible.
parseInt() parses only integers
parseFloat() prases both integers and floating-point numbers
If a string begins with "0x" or "0X", parseInt() interprets it as a hexadecimal number. Both parseInt() and parseFloat() skip leading whitespace, parse as many numeric characters as they can, and ignore anything that follows.If the first nonspace character is not part of a valid numeric literal, they return NaN:
例如:
parseInt("3 blind mice") // => 3
parseFloat(" 3.14 meters") // => 3.14
parseInt("-12.34") // => -12
parseInt("0xFF") // => 255
parseFloat(".1") // => 0.1
parseInt("0.1") // => 0
parseInt(".1") // => NaN: integers can't start with "."
parseFloat("$72.47"); // => NaN: numbers can't start with "$"
parseInt() accepts an optional second argument specifying the radix (base) of the number to be parsed.Legal values are between 2 and 36. For example:
parseInt("11", 2); // => 3 (1*2 + 1)
parseInt("ff", 16); // => 255 (15*16 + 15)
parseInt("zz", 36); // => 1295 (35 * 36 + 35)
parseInt("077", 8); // => 63 (7*8 + 7)
parseInt("077", 10); // => 77 (7*10 + 7)
将一个对象转换为一个string:
1. 首先查找对象是否有一个toString()方法，如果有，则调用他，如果没有或者没有返回一个原始值，则 =>
2. 查找对象是否有一个valueOf()方法，如果有，则调用，如果没有或者没有返回一个原始类型，则=>
3. 抛出TypeError
将一个对象转换为number:
是同样的3个步骤，但是首先查找valueOf()方法，其次才是toString()
Arrays:
Arrays inherit the default valueOf() method that returns an object rather than a primitive value, so array-to-number conversion relies on the toString() method.