Expressions

Expressions are a flexible data type that Xano parses in real-time to support an inline syntax to expressing data with mathematical expressions. Anything you can do with Xano filters, can also be done inline within an expression.

When building expressions, make sure you have the 'expression' data type selected. You can also click Use Expression under any value box to quickly switch.

Expression building in Xano leverages auto-complete, which will auto-populate references to inputs and variables, filters, and other common notation.

Mathematical Operators

Operator	Function	Example	Result
+	addition	100 + 101	201
-	subtraction	100 - 101	-1
*	multiplication	100 * 101	10101
/	division	100 / 10	10

Operator Precedence

For the most part expressions are evaluated left to right. Using parentheses to illustrate a point, the following would be the same assuming all operators were being evaluated left to right.

1 + 2 + 3     == 6
1 + (2 + 3)   == 6

However, there are a few operators which get special priority and get evaluated first. These operators are the multiplication and divide operators.

1 + 2 * 3    == 7          // if left to right, then 9 (which is incorrect)
1 + (2 * 3)  == 7

1 + 4 / 2    == 3          // if left to right, 2.5 (which is incorrect)
1 + (4 / 2)  == 3

Text Operators

Operator	Function	Example	Result
~	concatenation	a ~ b	ab

To add separation when concatenating, add an empty string between the values: ​a~" "~b

Array Operators

Operator	Function	Example	Result
...	spread items within an array	[1,2,3, ...[4,5,6],7]	[1,2,3,4,5,6,7]
..	range operator	1..10	[1,2,3,4,5,6,7,8,9,10]

Array Indexes

Expressions have the ability to reference array elements using all integer values (0, positive numbers, and negative numbers). Using a negative number represents starting from the top of the list rather the beginning of the list.

Expression	Result
[a,b,c,d,e][0]	a
[a,b,c,d,e][1]	b
[a,b,c,d,e][-1]	e
[a,b,c,d,e][-2]	d

Object Operators

Operator	Function	Example	Result
...	spread items within an object	{a:1, b:2, ...{c:3}, d: 4}	{a:1,b:2,c:3,d:4}

Comparison Operators

Operator	Function	Example	Result
==	equals (type conversion)	1 == "1"	true
===	strict equals	1 === "1"	false
!=	not equals (type conversion)	1 != "1"	false
!==	strict not equals	1 !== "1"	true
>	greater than	1 > 2	false
>=	greater than or equals	1 >= 2	false
<	less than	1 < 2	true
<=	less than or equals	1 <= 2	true

Logical Operators

Operator	Function	Example	Result
!	not	!true	false
||	or	1 < 2 || 1 != 1	true
&&	and	1 < 2 && 1 != 1	false

All of these operators evaluate their expressions as truthy statements. This means that a comparison operator is not required. For example: 0 || 1 would evaluate to true since 1 evaluates as true.

Conditional Operators

Operator	Function	Example	Result
a ? b : c	ternary (if/else)	1 < 2 ? 3 : 4	3
a ?: b	shorthand ternary (this/that)	1 ?: 2	1
a ?? b	null coalescing	null ?? 10	10

The ternary operator has 2 forms - the traditional if/else based on expression and the shorthand (this/that). The shorthand version will use either the left (this) or the right (that) based on which one evaluates to a truthy statement first going from left to right.

The null coalescing operator is very similar to the shorthand ternary, except that instead of relying on a truthy statement, it only checks for the null value.

Variable Syntax

Variables can be referenced using the same syntax that is available within Lambdas.

Variables

Variables within the function stack are accessible through $var root variable.

Inputs

Inputs are accessible through the $input root variable.

Authentication

Authentication values are accessible through the $auth root variable.

Environment Variables

Environment variables are accessible through the $env root variable. This includes both system variables ($remote_ip, $datasource, etc.) as well as workspace environment variables.

Auto-Complete

When building expressions, you'll see autocomplete suggestions as you type. This works for variables, inputs, and environment variables, as well as filters.

For variables with nested data, such as objects, you'll also be presented with an auto-complete of the fields inside of that object. In this example, we're targeting a variable called logand are presented with the fields inside of that variable by the expression builder, as well as a description of each.

Data Types

The Xano expression engine supports a more relaxed syntax for its data types to make it easier to reference text and variables without the strict requirements of using quotation marks.

Expression	Type	Result
abc	text	"abc"
123	integer	123
$var.score	integer	123
"$var.score"	text	"$var.score"
"\""	text with escaped character	"
true	boolean	true
false	boolean	false
"true"	text	"true"
null	null	null
"null"	text	"null"
"123"	text	"123"
[1,2,3]	array of integers	[1,2,3]
["1","2","3"]	array of text	["1","2","3"]
[a,b,c]	array of text	["a","b","c"]
["a","b","c"]	array of text	["a","b","c"]
{a:1}	object	{"a":1}
{"a":a}	object	{"a":"a"}
{"a":$var.score}	object	{"a":123}

Dot Notation

The same relaxed syntax used for data types also applies to dot notation.

Dot Notation	JSON Equivalent
$var.items	$var.items
$var.items[1]	$var.items[1]
$var.items["1"]	$var.items["1"]
$var.items[a]	$var.items["a"]
$var.items[a~b~c]	$var.items["abc"]
$var.items["a~b~c"]	$var.items["a~b~c"]

Filters

All of the Xano filters are available within the expression syntax. To use these, you need to follow the pipe expression syntax.

variable | pipe : arg1 : arg2 : argN

For example, to uppercase text using the upper filter, you would do the following.

"xano"|upper

// result = XANO

Here is another example using a filter with an argument.

1 + 2 + (3|add:1)

// result = 7

This particular example is using both a mathematical "+" and an add filter to illustrate how they can be mixed together.

You can also chain filters together.

1 + 2 + (3|add:1|mul:2)

// result = 11

Importing Expressions

When importing cURL or pasting JSON into Xano, Xano can automatically detect the Expression data type, provided the expression begins with a $ character.

As an example, the following JSON...

{"id":"0a1612ca-37d3-4d45-85ad-841a7522e000","created_at":"$test.0.id"}

...will import as:

Advanced Examples

As showcased above, the Xano expression engine is very powerful. Here we can look into some more advanced use cases that bring everything together.

Conditional

Sample Data

$input = {
  "scores": [1,2,3]
}

$var = {
  "numbers": [4,5,6]
}

Expression

($input.scores|max) > ($var.numbers|min)

// result = false

Null coalescing

Sample Data

$input = {
  "scores": [1,2,3]
}

$var = {
  "numbers": [4,5,6]
}

Expression

(($input.scores|merge:[100,101,102])|max)+($var.bad_syntax ?? 100)

// result = 202

Ternary

Sample Data

$input = {
  "scores": [1,2,3]
}

$var = {
  "numbers": [0,1,2,3,4,5,6]
}

Expression

($input.scores[2] == 3 ? 10 : 100) + (($var.numbers|min) ?: $var.numbers|max))

// result = 16