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sprintf-js
sprintf-js is a complete open source JavaScript sprintf
implementation for the browser and Node.js.
Note: as of v1.1.1 you might need some polyfills for older environments. See Support section below.
Usage
var sprintf = require('sprintf-js').sprintf,
vsprintf = require('sprintf-js').vsprintf
sprintf('%2$s %3$s a %1$s', 'cracker', 'Polly', 'wants')
vsprintf('The first 4 letters of the english alphabet are: %s, %s, %s and %s', ['a', 'b', 'c', 'd'])
Installation
NPM
npm install sprintf-js
Bower
bower install sprintf
API
sprintf
Returns a formatted string:
string sprintf(string format, mixed arg1?, mixed arg2?, ...)
vsprintf
Same as sprintf
except it takes an array of arguments, rather than a variable number of arguments:
string vsprintf(string format, array arguments?)
Format specification
The placeholders in the format string are marked by %
and are followed by one or more of these elements, in this order:
- An optional number followed by a
$
sign that selects which argument index to use for the value. If not specified, arguments will be placed in the same order as the placeholders in the input string. - An optional
+
sign that forces to precede the result with a plus or minus sign on numeric values. By default, only the-
sign is used on negative numbers. - An optional padding specifier that says what character to use for padding (if specified). Possible values are
0
or any other character preceded by a'
(single quote). The default is to pad with spaces. - An optional
-
sign, that causessprintf
to left-align the result of this placeholder. The default is to right-align the result. - An optional number, that says how many characters the result should have. If the value to be returned is shorter than this number, the result will be padded. When used with the
j
(JSON) type specifier, the padding length specifies the tab size used for indentation. - An optional precision modifier, consisting of a
.
(dot) followed by a number, that says how many digits should be displayed for floating point numbers. When used with theg
type specifier, it specifies the number of significant digits. When used on a string, it causes the result to be truncated. - A type specifier that can be any of:
%
— yields a literal%
characterb
— yields an integer as a binary numberc
— yields an integer as the character with that ASCII valued
ori
— yields an integer as a signed decimal numbere
— yields a float using scientific notationu
— yields an integer as an unsigned decimal numberf
— yields a float as is; see notes on precision aboveg
— yields a float as is; see notes on precision aboveo
— yields an integer as an octal numbers
— yields a string as ist
— yieldstrue
orfalse
T
— yields the type of the argument<sup><a href="#fn-1" name="fn-ref-1">1</a></sup>v
— yields the primitive value of the specified argumentx
— yields an integer as a hexadecimal number (lower-case)X
— yields an integer as a hexadecimal number (upper-case)j
— yields a JavaScript object or array as a JSON encoded string
Features
Argument swapping
You can also swap the arguments. That is, the order of the placeholders doesn't have to match the order of the arguments. You can do that by simply indicating in the format string which arguments the placeholders refer to:
sprintf('%2$s %3$s a %1$s', 'cracker', 'Polly', 'wants')
And, of course, you can repeat the placeholders without having to increase the number of arguments.
Named arguments
Format strings may contain replacement fields rather than positional placeholders. Instead of referring to a certain argument, you can now refer to a certain key within an object. Replacement fields are surrounded by rounded parentheses - (
and )
- and begin with a keyword that refers to a key:
var user = {
name: 'Dolly',
}
sprintf('Hello %(name)s', user) // Hello Dolly
Keywords in replacement fields can be optionally followed by any number of keywords or indexes:
var users = [
{name: 'Dolly'},
{name: 'Molly'},
{name: 'Polly'},
]
sprintf('Hello %(users[0].name)s, %(users[1].name)s and %(users[2].name)s', {users: users}) // Hello Dolly, Molly and Polly
Note: mixing positional and named placeholders is not (yet) supported
Computed values
You can pass in a function as a dynamic value and it will be invoked (with no arguments) in order to compute the value on the fly.
sprintf('Current date and time: %s', function() { return new Date().toString() })
AngularJS
You can use sprintf
and vsprintf
(also aliased as fmt
and vfmt
respectively) in your AngularJS projects. See demo/
.
Support
Node.js
sprintf-js
runs in all active Node versions (4.x+).
Browser
sprintf-js
should work in all modern browsers. As of v1.1.1, you might need polyfills for the following:
String.prototype.repeat()
(any IE)Array.isArray()
(IE < 9)Object.create()
(IE < 9)
YMMV
License
sprintf-js is licensed under the terms of the BSD 3-Clause License.
Notes
<small><sup><a href="#fn-ref-1" name="fn-1">1</a></sup> sprintf
doesn't use the typeof
operator. As such, the value null
is a null
, an array is an array
(not an object
), a date value is a date
etc.</small>