string-format

string-format is a small JavaScript library for formatting strings, based on
Python's [str.format()][1]. For example:

``javascript
'"{firstName} {lastName}" <{email}>'.format(user)
// => '"Jane Smith" '
`

The equivalent concatenation:

`javascript
'"' + user.firstName + ' ' + user.lastName + '" <' + user.email + '>'
// => '"Jane Smith" '
`

$3

#### Node

1. Install:

`console
$ npm install string-format
`

2. Require:

`javascript
const format = require('string-format')
`

#### Browser

1. Define window.format:

`html

`

$3

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

#### Function mode

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

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

#### Method mode

`javascript
'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:

`javascript
format.extend(String.prototype, {})
`

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

$3

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

Placeholders may contain numbers which refer to positional arguments:

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

Unmatched placeholders produce no output:

`javascript
'{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:

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

Positional arguments may be referenced implicitly:

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

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

`javascript
'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 }:

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

Dot notation may be used to reference object properties:

`javascript
const bobby = {firstName: 'Bobby', lastName: 'Fischer'}
const 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}:

`javascript
const 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:

`javascript
const sheldon = {
firstName: 'Sheldon',
lastName: 'Cooper',
dob: new Date('1970-01-01'),
fullName: function() { return this.firstName + ' ' + this.lastName },
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!"
`

$3

This function takes an object mapping names to transformers and returns a
formatting function. A transformer is applied if its name appears, prefixed
with !, after a field name in a template string.

`javascript
const fmt = format.create({
escape: s => s.replace(/[&<>"']/g, c => '&#' + c.charCodeAt(0) + ';'),
upper: s => s.toUpperCase(),
})

fmt('Hello, {!upper}!', 'Alice')
// => 'Hello, ALICE!'

const restaurant = {name: 'Anchor & Hope', url: 'http://anchorandhopesf.com/'}

fmt('{name!escape}', restaurant)
// => 'Anchor & Hope'
``

$3

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

`javascript
format.extend(String.prototype, {
escape: s => s.replace(/[&<>"']/g, c => '&#' + c.charCodeAt(0) + ';'),
upper: s => s.toUpperCase(),
})

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

const restaurant = {name: 'Anchor & Hope', url: 'http://anchorandhopesf.com/'}

'{name!escape}'.format(restaurant)
// => 'Anchor & Hope'
``

$3

`console
$ npm install
$ npm test
``

[1]: http://docs.python.org/library/stdtypes.html#str.format