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Expressions can be used in Snaps such as the Mapper (Data) Snap to manipulate data. The expressions are based off a subset of JavaScript and act accordingly unless otherwise noted.

See Using Expressions for specifics on how to enter expressions.


Comparison Operators

Comparison operators (>, >=, <, <=, ==, !=) behave the same as JavaScript comparison operators except that strict equals (===) and strict not equals (!===) are not supported.

Arithmetic Operators

Arithmetic operators (+, -, *, /) operators behave the same as JavaScript arithmetic operators except that increment (++) and decrement (--) are not supported.


All arithmetic operators return a floating point number. If an integer is desired, then the global function {{parseInt}} should be used to cast the arithmetic expression as an integer.

1/2 = .5
parseInt(1/2) = 0

Logical Operators

Logical operators (&&, ||, !) behave the same as JavaScript logical operators

String Operators

String operators (+) behave the same as JavaScript string operators except that the shorthand assignment operator (+=) is not supported.

Spread Operators

The spread operator (...) makes it easier to build arrays, objects, and call functions where the list of arguments is built at runtime. For instance, while using in an array literal, the value on the right of the operator is inserted into the new array at that position. Similarly, in a function call, the array expands and is used as the arguments to the function. In an object literal, the right side of the operator is another object that has its keys added to the new object.


To build a new array that is made up of another array surrounded by two elements:

Code Block
["header", ...$body, "footer"]

If you want to find the maximum value in an array of numbers:

Code Block

To create a new object with some fixed values and entries in the "$extra" object:

Code Block
{ first_name: $fname, last_name: $lname, ... $extra }

Special Operators


Conditional (Ternary)

The conditional operator (?) allows you to specify a value to use based on the result of an expression. The syntax is as follows:

Code Block
condition ? trueValue : falseValue

The condition expression will be evaluated and the trueValue will be the result of the expression if the condition evaluates to true, otherwise the falseValue will be the result.


Code Block
$text == "NFL" ? "foo" : "bar"


Code Block
$counter > 1 ? ($counter < 3 ? 50 : 100) : -1



The instanceof operator returns True if the given object is an instance of the given type. The syntax is as follows:

Code Block
object instanceof type

The possible values for the type are: Null, Boolean, String, Number, Object, Array, Date, LocalDate, DateTime, and LocalDateTime.


Code Block
$my_array instanceof Array 



The match operator allows you to conditionally evaluate one of a number of expressions based on whether an input value matches a given pattern.  See the match Control Flow Operator section to learn more.


Paste code macro
match $score {
    90..=100 => 'A',
    80..<90 => 'B',
    70..<80 => 'C',
    _ => 'F'



The typeof operator returns the type of a value as a string. The syntax is as follows:

Code Block
typeof operand

The possible return values are: "boolean", "number", "string", "object", and "array".



The in operator returns true if the property name or array index is in the given object or array. The syntax is as follows:

Code Block
name|index in operand


Code Block
'name' in $ 


You can add notes to your expressions using comments.  A comment starts with '/*' and ends with '*/', for example:

Code Block
/* say hello */ "Hello, World!"

The comment will be ignored when evaluating the expression, it is only for the reader's benefit.

Operator Precedence

Operator typeIndividual operators
member. []
negation! -
multiply/divide* / %
addition/subtraction+ -
relational< <= > >=
equality== !=

Unsupported Operations

  • Assignment 
    • Creating variables and assigning values is not supported 
    • Example: var temp = 10
  • Short hand assignment
    • Example: count += 5
  • Strict equals
    • Example: first === last
  • Strict not equals
    • Example: first !== last
  • Increment
    • Example: count++
  • Decrement
    • Example: count--

Accessing Document Values

To access values in a document, JavaScript object accessors can be used.
For a given document data:

Code Block
    first_name: "James",
    last_name: "Smith"

The expression $first_name would return the 'first_name' property which is James.
The 'first_name' property can also be accessed by using array notation $['first_name'].
JavaScript array accessors can be used also if the object is an array/list.
For a given document data:

[ 1, 2, 3]

$[1] would return the value 2.

More complex example:

Code Block
    names: ["Joe", "Bob", "Fred"]

$names[2] would return the value Fred.

Arrow Functions

Custom expression language functions can be created using the arrow function syntax:

Code Block
// A function that takes multiple parameters:
(param1, param2, ..., paramN) => expression

// A function that takes a single parameter does not need parentheses:
(param) => expression
param => expression

// A function with no parameters requires parentheses:
() => expression

// Function parameters can also have default values
(param1 = defaultValue1, param2 = defaultValue2, ..., paramN = defaultValueN) => expression

These functions can be passed to other functions that accept callbacks, like or Array.filter(), or they can be put into an expression library for use in any expression property in your pipelines.


To multiply all numbers in an array by ten:
[1, 2, 3].map(x => x * 10)


  [10, 20, 30]


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