Built-in Functions
The expression engine provides whitelisted functions for math, dates, and data utilities. Only these functions are available — arbitrary JavaScript functions cannot be called.
Math functions
All functions are accessed via the Math object.
| Function | Description | Example | Result |
|---|---|---|---|
Math.abs(n) | Absolute value | {{Math.abs(-5)}} | 5 |
Math.ceil(n) | Round up | {{Math.ceil(4.2)}} | 5 |
Math.floor(n) | Round down | {{Math.floor(4.8)}} | 4 |
Math.round(n) | Round to nearest integer | {{Math.round(4.5)}} | 5 |
Math.max(a, b) | Larger of two values | {{Math.max(price, minPrice)}} | whichever is larger |
Math.min(a, b) | Smaller of two values | {{Math.min(score, 100)}} | caps at 100 |
Math.sqrt(n) | Square root | {{Math.sqrt(16)}} | 4 |
Math.pow(a, b) | Power | {{Math.pow(2, 3)}} | 8 |
Math.trunc(n) | Truncate decimal | {{Math.trunc(4.9)}} | 4 |
Practical examples
// Cap a value between 0 and 100
{{Math.min(Math.max(score, 0), 100)}}
// Round a price to avoid floating point issues
{{Math.round(price * 100) / 100}}
// Calculate distance
{{Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2))}}Date functions
All functions are accessed via the Date object.
| Function | Description | Example | Result |
|---|---|---|---|
Date.now() | Current timestamp (ms) | {{Date.now()}} | 1708876800000 |
Date.parse(value) | Parse date string to timestamp | {{Date.parse(createdAt)}} | timestamp in ms |
Date.format(value, fmt) | Format a date | {{Date.format(createdAt, "YYYY-MM-DD")}} | "2024-02-25" |
Date.format only supports two format strings:
"YYYY-MM-DD"— returns"2024-02-25"- Any other value — returns full ISO string
"2024-02-25T12:00:00.000Z"
There is no support for custom format patterns like "MM/DD/YYYY" or "HH:mm:ss".
Practical examples
// Format a timestamp to date
{{Date.format(updatedAt, "YYYY-MM-DD")}}
// Check if a date is in the past
{{Date.parse(expiresAt) < Date.now()}}Utility functions
These are available as top-level functions (no object prefix).
| Function | Description | Example | Result |
|---|---|---|---|
stringify(value) | Convert to JSON string | {{stringify(address)}} | '{"city":"NYC"}' |
toString(value) | Convert to string | {{toString(count)}} | "42" |
keys(value) | Get object keys | {{keys(user)}} | ["name","age"] |
values(value) | Get object values | {{values(user)}} | ["Alice",25] |
stringify(value)
Converts any value to its JSON string representation using JSON.stringify. Useful for serializing nested objects into a flat string.
// Input: { "meta": { "version": 2, "draft": true } }
{{stringify(meta)}} → '{"version":2,"draft":true}'toString(value)
Converts a value to a string. Handles special cases:
null/undefined→""(empty string)Dateobjects → ISO string- Objects → JSON string (same as
stringify) - Everything else →
String(value)
{{toString(42)}} → "42"
{{toString(null)}} → ""
{{toString(true)}} → "true"keys(value) and values(value)
Return the keys or values of an object as arrays. Returns an empty array for non-objects.
// Input: { "user": { "name": "Alice", "age": 25, "role": "admin" } }
{{keys(user)}} → ["name", "age", "role"]
{{values(user)}} → ["Alice", 25, "admin"]Since single expressions preserve types, {{"{{"}}keys(user){{"}}"}} returns an actual array, not a string. This is useful when the result feeds into another operation.