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Variable Filters #

Used to modify variables. Filters are added directly after variable names, separated by the pipe (|) character. You can chain multiple filters together, applying one after the other in succession.


{{ name|title }} was born on {{ birthday|date('F jS, Y') }} and has {{ bikes|length|default("zero") }} bikes.

Filters can also be applied to blocks of content directly with the filter tag.

{% filter uppercase %}oh hi, paul{% endfilter %}

Built-In Filters #\

add(value) #

Adds the value to the variable. Strings that can be converted to integers will be summed, not concatenated, as in the example below.


  1. value (mixed) The value to add to the variable before printing it to the page. Accepts any array, object, number, and string.

addslashes #

Returns a string with backslashes in front of characters that need to be quoted for database queries, etc.

  • single quote '
  • double quote "
  • backslash \

capitalize #

Capitalize the first character in the string.

date(format) #

Convert a valid date into a format as specified. Mostly conforms to's date formatting.


  1. format (string) The format to convert the date to. See the date formatting table.
  2. tzOffset (number) The timezone offset in minutes from GMT to display the date in.
    • For example, if your server is running in PDT, but you want to display your dates in CDT, set this to 360.
    • This can also be set globally via config variable tzOffset on swig.init.
Date formatting character information from
Format Character Description Example Output
d Day of the month, 2 digits with leading zeros 01 - 31
D A textual representation of a day, three letters Mon - Sun
j Day of the month without leading zeros 1 - 31
l A full textual representation of the day of the week Monday - Sunday
N ISO-8601 numeric representation of the day of the week 1 - 7 (Monday - Sunday)
S English ordinal suffix for the day of the month, 2 characters st, nd, rd, or th
w Numeric representation of the day of the week 0 - 6 (Sunday - Saturday)
z The day of the year starting from 0 0 - 365 (January 1st - December 31st [only on leap year])
W ISO-8601 week number of the year 42
F A full textual representation of a month, such as January or March January - December
m Numeric representation of a month, with leading zeros 12 - 01
M A short textual representation of a month, three letters Jan - Dec
n Numeric representation of a month, without leading zeros 1 - 12
t Number of days in the given month 28 - 31
L Whether or not the given year is a leap year. true or false
o ISO-8601 year number. This has the same value as Y, except that if the ISO week number (W) belongs to the previous or next year, that year is used instead. 1999
Y A full numeric representation of a year, 4 digits 1999
y A two digit representation of a year 99
a Lowercase Ante meridiem and Post meridiem am or pm
A Uppercase Ante meridiem and Post meridiem AM or PM
B Swatch Internet Time 000 - 999
g 12-hour format of an hour without leading zeros 1 - 12
G 24-hour format of an hour without leading zeros 0 - 23
h 12-hour format of an hour with leading zeros 01 - 12
H 24-hour format of an hour with leading zeros 00 - 23
i Minutes with leading zeros 00 - 59
s Seconds, with leading zeros 00 - 59
O Difference to Greenwich time (GMT) in hours +0200
Z Timezone offset in seconds. The offset for timezones west of UTC is always negative, and for those east of UTC is always positive. -43200 - 50400
Full Date & Time
c ISO 8601 formatted date 2011-09-06T16:05:02.000Z
r RFC 2822 formatted date Tue, 06 Sep 2011 16:05:02 GMT
U Seconds since the Unix Epoch (January 1 1970 00:00:00 GMT) 1315690513

default(value) #

If the variable is undefined, null, or false, a default return value can be specified.


  1. value (mixed) Fallback value if the variable is falsy.

escape([type]) / e([type]) #

Force escape the output of the variable. Optionally use e as a shortcut filter name. This filter will be applied by default if autoescape is turned on.

Default, HTML Variable Replacements

Character Replacement
& &
< &lt;
> &gt;
" &quot;
' &#39;

JavaScript Variable Replacements

Pass js as the type to your escape filter to toggle escaping as JavaScript.

Character Replacement
ASCII charCodes less than 32
\u0001 - \u001F
& \u0026
< \u003C
> \u003E
' \u0027
" \u0022
= \u003D
- \u002D
; \u003B


  1. type (string) optional passing "js" as the type will force JavaScript-safe escaping.

first #

Returns the first element of an array. Uses underscore.js first

join(glue) #

If the value is an Array, you can join each value with a delimiter and return it as a string.


  1. glue (string) Concatenation string to join each item in the array with.

json_encode #

Return a JSON string of the variable.

last #

Returns the last element of an array. Uses underscore.js last

length #

Return the length property of the variable. If the variable is an object, this will return the length of the keys on the object.

lower #

Return the variable in all lowercase letters.

raw #

Do not escape the output of the variable.

replace(search, replace[, flags]) #

Uses built-in JavaScript replace method. Provide a regular-expression or a string and a replacement string.


  1. search (string) string converted to a regular expression. Example: '\s' will become /\s/, while 's' will become /s/
  2. replace (string) a string to replace the matched parts from search
  3. flags (string) optional Regular expression flags. [reference]

reverse #

If the value is an Array, this filter will reverse all items in the array.

striptags #

Strip all HTML/XML tags.

title #

Change the output to title case–the first letter of every word will uppercase, while all the rest will be lowercase.

uniq #

Produces a duplicate-free version of the array. Uses underscore.js uniq

upper #

Return the variable in all uppercase letters

url_encode #

Encode a URI component.

url_decode #

Decode a URI component.

Writing Custom Filters #

Custom filters are very easy to write for your own project that uses Swig.

Create a file called myfilters.js and include it in the Swig init function:

swig.init({ filters: require('myfilters') });

In your myfilters.js file, each filter method is just a simple javascript method. For example, here's a filter to make a variable all lowercase:

exports.lower = function (input) {
    return input.toString().toLowerCase();

For more examples, view the filters.js source file

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