Fōmatto - Japanese for Format

Fōmatto provides leightweight string interpolation and formatting for JavaScript.

The library brings with it the Formatter factory and the FormatError.

Usage

In order to use Fōmatto it is necessary to create a format function with the Formatter factory.

Formatter([formats])

The format function

format(template, arg1[, arg2, arg3, ...argN])

The format function takes a template and either multiple arguments, an array or array like object (an object with a length property of type Number) or a standard object as its arguments.

> format('Good {} Sir {}.', 'morning', 'Lancelot')
'Good morning Sir Lancelot.'

> format('Good {0} Sir {1}.', 'morning', 'Lancelot')
'Good morning Sir Lancelot.'

> format('Good {time} Sir {name}.', 'morning', 'Lancelot')
'Good morning Sir Lancelot.'

> format('Good {0} Sir {1}.', ['morning', 'Lancelot'])
'Good morning Sir Lancelot.'

> format('Good {time} Sir {name}.', {time: 'morning', name: 'Lancelot'})
'Good morning Sir Lancelot.'

> format('Good {0} Sir {1}.', {0: 'morning', 1: 'Lancelot', length: 2})
'Good morning Sir Lancelot.'

Templates

String templates contain placeholders wrapped in {}. There are a number of different ways in which these placeholders can be used to insert data into a template.

• Auto indexes via {}, these automatically insert the next item from an array or a list of arguments.

• Positive {1} or negative {-1} indexes, these will insert the Nth or length + Nth index of an array or a list of arguments.

• Property access via {name}, these will either insert the corresponding property of an object or behave like auto indexes in case of an array or a list of arguments.

• Complex property access via {users.names[2]['first']}, these will query an object for the specified property and throw a FormatError in case the property could not be resolved.

Formats

By appending a semicolon at the end of a placeholder it is possible to apply a formatting function to the value before it is inserted.

> format('{0:upper}!', 'banana')
'BANANA!'

> format('Some fruits: {:join(', ')}!', ['melons', 'oranges', 'strawberries'])
'Some fruits: melons, oranges, strawberries!'

Standard formats

• upper will transform to UPPER case.
• lower will transform to lower case.
• lpad(count [, padding=' ']) will pad to count characters on the left side.
• rpad(count [, padding=' ']) will pad to count characters on the right side.
• pad(count [, padding=' ']) will equally pad to count characters on both sides.

Note: The pad formats only support single characters for padding.

• surround(left=' ' [, right=left]) will surround with left and right.

• repeat(count=0) will repeat count times.

• join([character=' ']) will join an array with character.

• hex([leading=false]) will convert to hexadecimal representation. If leading is true 0x will be prepended.

• bin([leading=false]) will convert to binary representation. If leading is true 0b will be prepended.

Custom formats

Using the Formatter factory one can add their own formatters.

var custom = Formatter({
    unicorns: function(value) {
        return value + ' unicorns!';
    }
});

> custom('Here come the {:unicorns}', 'five')
'Here come the five unicorns!'

It is also possible to add more formats later on by setting properties on the formats object of a format function.

custom.formats.foo = function(value) {
    return 'foo';
};

This will add the format :foo.

Adding default formats

By extending Formatter.formats it's also possible to add more default formats.

Formatter.formats.bonsai = function(value) {
    // ...   
};

The format :bonsai will now be available to all format functions.