StringFormat

Description

This module provides a simple function that can be used to format strings, using replacements such as {0}, {foo}, etc.

Features

• Node/browser compatible.
  • In the browser, it gets installed as window.stringformat (call window.stringformat.extendString() to install the String.format() method).
• Order-independent replacements, so that format strings can be localized.
  • Example: Hello {firstname} {lastname} in English, こんにちは、{lastname}{firstname}さん in Japanese.
• Can pass one or several objects, and use property names instead of numbers.
• Support modifiers to output values as integers or JSON.
• Opt-in String.prototype extension (using extendString())

Install

npm install stringformat

API

stringformat(format string, parameters...)

Returns a new string formatted according to format string.

Example usage:

var stringformat = require('stringformat')
console.log(stringformat("Hello, {0}!", "World"))

…would output Hello, World! to the console.

stringformat.extendString([methodName])

Installs the module as String.prototype.methodName. If omitted, methodName defaults to format.

Example usage:

var stringformat = require('stringformat')
 
stringformat.extendString('coolFormat')
console.log("Hello, {0}!".coolFormat("World"))

…would output Hello, World! to the console.

Format strings syntax

All the examples shown below assume stringformat.extendString() has been called.

Basic replacements

The most simple replacements look like {0}, {1} and so on. The number is the index of the parameter.

"Hello, {1}! I feel {0} today!".format("great", "World")
'Hello, World! I feel great today!'

You can also use functions:

"Hello, {1}! I feel {0} today!".format("great", function() { return "World" })
'Hello, World! I feel great today!'

var x = 0
"{0} {0} {0}…".format(function() { return ++x })
'1 2 3…'

If a replacement cannot be resolved, the method does nothing:

"Hello, {1}! I feel {0} today!".format("great")
'Hello, {1}! I feel great today!'

Padding

If you want to pad the result, for instance to print a list of values, you can do it like this:

"User name: [{0:20}]".format("Bob Harris")
'User name: [          Bob Harris]'

…this gives you a replaced content that is at least 20 characters wide. Positive integers mean the value will get right-aligned. To align it to the left, use a negative value:

"User name: [{0:-20}]".format("Bob Harris")
'User name: [Bob Harris          ]'

The JSON modifier

If you want to output a JSON version of the value, you can use it with the j modifier. Compare the output above with the one below:

"User name: {0:j}".format("Bob Harris")
'User name: "Bob Harris"'

Of course you can use objects slightly more complex than a string:

"User name: {0:j}".format({foo:{bar:1}})
'User name: {"foo":{"bar":1}}'

…or even a function:

"User name: {0:j}".format(function() { return {foo:{bar:1}} })
'User name: {"foo":{"bar":1}}'

The integer modifier

If you want to output integer values only, use the i modifier. Floating values will get rounded, and values that are not numbers will output NaN.

"value = {0:i}".format(12.5)
'value = 13'

"[value:{0:4i}]".format(12.5)
'[value:  13]'

"[value:{0:4i}]".format("foo")
'[value: NaN]'

"[value:{0:4i}]".format()
'[value: NaN]'

"[value:{0:4i}]".format(function() { var undef; return undef })
'[value: NaN]'

As an exception to the rule mentioned above,

If a replacement cannot be resolved, the method does nothing

…if the integer modifier is specified, unresolved replacements will result in a NaN being outputted.

Named properties

You can also use names instead of indexes.

"[{foo:-4i}]".format({foo:1})
'[1   ]'

"[{foo.bar:-4i}]".format({foo:{bar:1}})
'[1   ]'

"The string {0:j} is {length}-character long".format("Hello, World!")
'The string "Hello, World!" is 13-character long'

var Foo = function() {
    this.foo = 1
}
"[{foo:-4i}]".format(new Foo)
'[1   ]'

var Foo = function() {
    this.foo = 1
}
Foo.prototype.bar = function() { return this.foo + 1 }
"[{bar:-4i}]".format(new Foo)
'[2   ]'

If you specify a property as foo.bar.baz and baz is a function, this will be equal to foo.bar when it gets called. And if either foo or bar were functions, too, they will be evaluated in turn!

"[{foo.bar.baz:4i}]".format({
    foo: function() {
        return {
            bar: {
                value: 1,
                baz: function() {
                    return this.value
                }
            }
        }
    }
})
'[   1]'

Accessing properties from multiple objects

Each replacement can be prefixed with an object index followed by a pipe symbol.

"[{0|foo.bar:4}] [{1|foo.bar:4}]".format({foo:{bar:4}}, {foo:{bar:8}})
'[   4] [   8]'

Escaping

Replacement specifiers can be escaped by doubling the opening and closing braces:

"{{0}} is [{0}]".format(1)
'{0} is [1]'

Running the tests

Clone this repository somewhere, then do:

$ npm install
$ npm test

License

(The MIT License)

Copyright (c) 2012 Julien Cayzac julien.cayzac@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.