string-format

Adds a format method to String.prototype. Inspired by Python's str.format().

String::format

String::format is a small JavaScript library for formatting strings, based on Python's str.format(). For example:

'"{firstName} {lastName}" <{email}>'.format(user)
// => '"Jane Smith" <jsmith@example.com>' 

The equivalent concatenation:

'"' + user.firstName + ' ' + user.lastName + '" <' + user.email + '>'
// => '"Jane Smith" <jsmith@example.com>' 
  1. Install:

    $ npm install string-format
    
  2. Require:

    var format = require('string-format')
    
  1. Define window.format:

    <script src="path/to/string-format.js"></script>
    

String::format can be used in two modes: function mode and method mode.

format('Hello, {}!', 'Alice')
// => 'Hello, Alice!' 

In this mode the first argument is a template string and the remaining arguments are values to be interpolated.

'Hello, {}!'.format('Alice')
// => 'Hello, Alice!' 

In this mode values to be interpolated are supplied to the format method of a template string. This mode is not enabled by default. The method must first be defined via format.extend:

format.extend(String.prototype)

format(template, $0, $1, …, $N) and template.format($0, $1, …, $N) can then be used interchangeably.

Returns the result of replacing each {…} placeholder in the template string with its corresponding replacement.

Placeholders may contain numbers which refer to positional arguments:

'{0}, you have {1} unread message{2}'.format('Holly', 2, 's')
// => 'Holly, you have 2 unread messages' 

Unmatched placeholders produce no output:

'{0}, you have {1} unread message{2}'.format('Steve', 1)
// => 'Steve, you have 1 unread message' 

A format string may reference a positional argument multiple times:

"The name's {1}. {0} {1}.".format('James', 'Bond')
// => "The name's Bond. James Bond." 

Positional arguments may be referenced implicitly:

'{}, you have {} unread message{}'.format('Steve', 1)
// => 'Steve, you have 1 unread message' 

A format string must not contain both implicit and explicit references:

'My name is {} {}. Do you like the name {0}?'.format('Lemony', 'Snicket')
// => ValueError: cannot switch from implicit to explicit numbering 

{{ and }} in format strings produce { and }:

'{{}} creates an empty {} in {}'.format('dictionary', 'Python')
// => '{} creates an empty dictionary in Python' 

Dot notation may be used to reference object properties:

var bobby = {firstName: 'Bobby', lastName: 'Fischer'}
var garry = {firstName: 'Garry', lastName: 'Kasparov'}
 
'{0.firstName} {0.lastName} vs. {1.firstName} {1.lastName}'.format(bobby, garry)
// => 'Bobby Fischer vs. Garry Kasparov' 

0. may be omitted when referencing a property of {0}:

var repo = {owner: 'davidchambers', slug: 'string-format'}
 
'https://github.com/{owner}/{slug}'.format(repo)
// => 'https://github.com/davidchambers/string-format' 

If the referenced property is a method, it is invoked with no arguments to determine the replacement:

var sheldon = {
  firstName:  'Sheldon',
  lastName:   'Cooper',
  dob:        new Date('1970-01-01'),
  fullName:   function() { return '{firstName} {lastName}'.format(this) },
  quip:       function() { return 'Bazinga!' }
}
 
'{fullName} was born at precisely {dob.toISOString}'.format(sheldon)
// => 'Sheldon Cooper was born at precisely 1970-01-01T00:00:00.000Z' 
 
"I've always wanted to go to a goth club. {quip.toUpperCase}".format(sheldon)
// => "I've always wanted to go to a goth club. BAZINGA!" 

This function defines a format method on the provided prototype (presumably String.prototype). One may provide an object mapping names to transformers. A transformer is applied if its name appears, prefixed with !, after a field name in a template string.

format.extend(String.prototype, {
  escapefunction(s) {
    return s.replace(/[&<>"'`]/g, function(c) {
      return '&#' + c.charCodeAt(0) + ';'
    })
  },
  upperfunction(s) { return s.toUpperCase() }
})
 
'Hello, {!upper}!'.format('Alice')
// => 'Hello, ALICE!' 
 
var restaurant = {
  name: 'Anchor & Hope',
  url: 'http://anchorandhopesf.com/'
}
 
'<a href="{url!escape}">{name!escape}</a>'.format(restaurant)
// => '<a href="http://anchorandhopesf.com/">Anchor &#38; Hope</a>' 
$ npm install
$ npm test