k-data Built-in Functions

Functions available through <let use="functionName" params="...">.

Invocation Pattern

Each <let> performs one transformation on an existing value:

<let from="create_time" as="createdDate" use="dateFormat" params="'yyyy-MM-dd'" />
<let from="title" as="shortTitle" use="truncate" params='{"length":20,"ellipsis":"..."}' />
<let from="amount" as="amountText" use="currencyFormat" params='{"currency":"USD"}' />
<let from="page_number" as="prev_page" use="subtract" params="1" />

Attribute	Description
from	Input value or field path
as	Output variable name
use	Function name from the table below
params	JSON5: a single value, an object, or a format string wrapped in single quotes

When a function fails, most return null or the original input instead of throwing into the template layer.

Function Summary

Category	Functions
Auth	jwtDecode
Date	dateFormat
Currency	currencyFormat
Math	add, subtract, multiply, divide, modulo
Text	trim, lowercase, uppercase, truncate

dateFormat

params	Description
'"yyyy-MM-dd"'	Format template
'{"format":"yyyy-MM-dd","fallback":"--"}'	Format template with fallback

Input can be a DateTime, a parseable date string, and similar values.

currencyFormat

params	Description
omitted	Defaults to CNY
'"USD"' or '{"currency":"EUR"}'	Sets the currency code

If the input cannot be converted to a number, the original value is returned.

add / subtract / multiply / divide / modulo

Function	params	Description
Any of them	'"3"', '2', or '{"value":5}'	Right-hand operand
divide, modulo	Right-hand operand is 0	Returns null

Example for pagination links. Do not write {pageIndex - 1} directly inside k-attribute:

<let as="page_number" source="queryString" from="page_number" default="1" />
<let from="page_number" as="prev_page_number" use="subtract" params="1" />
<let from="page_number" as="next_page_number" use="add" params="1" />
<a k-attribute="href /products?page_number={prev_page_number}">Previous</a>

trim / lowercase / uppercase / truncate

<let from="keyword" as="normalizedKeyword" use="trim" />
<let from="title" as="shortTitle" use="truncate" params='{"length":20,"ellipsis":"..."}' />

For truncate, length <= 0 returns an empty string.

jwtDecode

Parses a JWT and optionally verifies its signature through params. A failed parse can be combined with a condition and redirect.

<k-data>
    <let as="token" source="cookie" from="access_token" default="''" />
    <let from="token" as="payload" use="jwtDecode" params='{"secret":"your-secret"}' export />
    <when test="{payload:{$eq:null}}">
        <redirect to="'/login'" />
    </when>
</k-data>

• Failure cases such as an empty token, invalid format, or failed verification return null.
• when test uses a JSON5 condition, not an ordinary expression such as payload == null.

Related

• Tag Syntax
• Condition Expressions