sprintf.js

sprintf.js is a javascript library used for formating string. The idea is from fmt.Sprintf of GoLang.

Usage

Note: This project is not a javascript model project. To use it please add the following code into your web page.

<script src="/path/of/sprintf.js"></script>

Printing

sprintf(formatedString, …args)

This function is similar as fmt.Sprintf of GoLang, sprintf() of C language, String.format() of Java... etc.

The formating rule is:

%    +0        4     .       2                f
    flag     width       presision     format specifier

flags

• 0

  pad with leading zeros rather than spaces; for numbers, this moves the padding after the sign

• #

  Please see v in “Format Specifier”.

• (space)

  leave a space for elided sign in numbers (% d); put spaces between bytes printing strings or slices in hex (% x, % X)

• +

  always print a sign for numeric values; guarantee ASCII-only output for %q (%+q)

• -

  pad with spaces on the right rather than the left (left-justify the field)

Format Specifier

sprintf() allows following format specifiers:

For Numbers

• b

  Convert the number to binery number.

• o

  Convert the number to octal numeral.

• d

  Convert the number to decimal integer.

• x

  Convert the number to hexadecimal number (lower case).

• X

  Convert the number to hexadecimal number (upper case).

• e

  Expressing the number by scientific notation (lower case).

• E

  Expressing the number by scientific notation (upper case).

• f / F

  Convert the number to a float number.

• g

  Convert the number. If it is a large exponents, it is same as %e. Otherwise %f.

• G

  Convert the number. If it is a large exponents, it is same as %E. Otherwise %f.

• U

  Expressing the number by unicode format (upper case). For example:

  sprintf("%U", 6896)    // return "U+1AF0"

• c

  If the argument is a number, it will be seen as a char code and be converted to the char; If it is a string, it will return the first char of the string.

  For example:

  sprintf("%c", 65)    // return "A"
  sprintf("%c", "ABC")    // return "A"

For String

• s

  Expressing the argument as a string

• q

  If the argument is a number, a single-quoted character literal safely escaped (same as sprintf("'%c'", arugment)). Otherwise, if it is a string, return a double-quoted string safely escaped (same as sprintf("\"%c\"", argument)).

  For example:

  sprintf("%q", 100)    // return "'d'"
  sprintf("%q", "d")    // return "\"d\""

For Boolean

• t

  Expressing a boolean.

Others

• T

  Return the type of the argument. If the argument is an object, it will return the name of its constructor.

  For example:

  sprintf("%T", 123)    // return "number"
  sprintf("%T", 123.4)    // return "number"
  sprintf("%T", "123")    // return "string"
  sprintf("%T", true)    // return "boolean"
  sprintf("%T", {a: 123})    // return "Object"
  sprintf("%T", [1, 23])    // return "Array"

• v

  Return the argument in default format

  The default format is:

  • decimal integer: d
  • float: f
  • string: s

  • Object:

    • If it is with # flag (%#v), convert the argument in JSON format
    • Otherwise, return the value of the argument’s toString().

  For example:

  sprintf("%v", 123)             // return "123"
  sprintf("%v", 123.456)         // return "123.4000"
  sprintf("%v", "Test")          // return "Test"
  sprintf("%v", {a:123, b:456})  // return "[object Object]"
  sprintf("%v", {
   a:123, 
   b:456,
   toString: function(){
       return "[MyObject]"
   }
  })                             // return "[MyObject]"
  sprintf("%#v", {a:123, b:456}) // return "{"a":123,"b":456}"

Explicit argument indexes

The default behavior is for each formatting verb to format successive arguments passed in the call. However, the notation [] immediately before the verb indicates that the nth one-indexed argument is to be formatted instead. For example:

sprintf("%[2]d", 11, 22)    // return "22"

The notation before a '' (`[]`) for a width or precision selects the argument index holding the value. For instance:

sprintf("%[2]*.[4]*[3]f", 11, 12, 13.123, 14, 15)

It is the same as

sprintf("%12.14[3]f")

Also, after processing a bracketed expression [n], subsequent verbs will use arguments n+1, n+2, etc. unless otherwise directed. For example:

sprintf("%[2]d    %d", 100, 200, 300)

It is the same as following code:

sprintf("%[2]d    %[3]d", 100, 200, 300)

For setting width or precision:

sprintf("%[2]*d", 100, 200, 300)

It is the same as following code:

sprintf("%[2]*[3]d", 100, 200, 300)