1. Convert numbers to Strings
A. To convert a number to a string, simply add an empty string to it:
Copy Code code as follows:
var n = 100;
var n_as_string = n + "";
B. To make the number more explicitly converted to a string, you can use the string () function:
Copy Code code as follows:
var string_value = string (number);
C. Use the ToString () method:
Copy Code code as follows:
String_value = Number.tostring ();
The Number object (the basic numbers are converted to the # object so that the method can be called) The ToString () method has an optional parameter that specifies the base of the conversion. If you do not specify this argument, the conversion is based on a 10 base. However, you can also convert numbers by the number of other cardinality (between 2 and 36).
For example:
Copy Code code as follows:
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"
The D. ToFixed () method converts a number to a string and displays the specified number of digits after the decimal point. It does not use exponential notation.
Copy Code code as follows:
var n = 123456.789;
n.tofixed (0); "123457"
N.tofixed (1); "123456.79"
E. toexponential () Converts a number to a string using exponential notation, preceded by a 1-digit number, with a specific number of digits following the decimal point.
Copy Code code as follows:
var n = 123456.789;
N.toexponential (1); "1.2e+5"
N.toexponential (3); "1.235e+5"
F. Toprecision () displays a number using the specified number of meaningful digits, which uses exponential notation if the meaningful number of digits is not sufficient to display the entire integer portion of the number.
Copy Code code as follows:
var n = 123456.789;
N.toprecision (4); "1.235e+5"
N.toprecision (7); "123456.8"
2. Converting strings to numbers
A. One of the missing tricks for converting a string to a number is clearly understood: the number () constructor is invoked as a function:
Copy Code code as follows:
var number = number (string_value);
B. parseint () only intercepts integers, if a string begins with "0x" or "0X", parseint () resolves it to a hexadecimal number, and parseint () can even accept a parameter to specify the cardinality of the number to parse, with a valid value between 2 and 36.
Copy Code code as follows:
parseint ("3 Blind Mice"); Returns 3
parseint ("12.34"); Returns 12
parseint ("0xFF"); Returns 255
parseint ("11", 2); Returns 3 (1 * 2 + 1)
parseint ("FF", 16); Returns 255 (15 * 16 + 15)
parseint ("ZZ", 36); Returns 1295 (35 * 36 + 35)
parseint ("077", 8); Returns 63 (7 * 8 + 7)
parseint ("077", 10); Returns 77 (7 * 10 + 7)
C. parsefloat () intercepts integers and floating-point numbers.
Copy Code code as follows:
Parsefloat ("3.14 meters"); Returns 3.14
D. If parseint () and parsefloat () cannot convert the specified string to numbers, they return Nan:
Copy Code code as follows:
parseint (' eleven '); Returns Nan
Parsefloat ("$72.47"); Returns NaN
3 Method of JavaScript rounding
A. Discard the fractional part and keep the whole number of parts
parseint (5/2)
B. Rounding up, with a decimal number on the integral part plus 1
Math.ceil (5/2)
C. Rounding down
Math.floor (5/2)
D. Rounding
Math.Round (5/2)
