Array Operations

The Array Operations block changes a list that you keep in a variable. You can add an item at the start or end, remove the first or last item, or keep only the items that match a rule.

When to use it

• Build up a list, like adding each result inside a For Each Loop.
• Keep a queue: add to the end (push) and take from the front (shift).
• Keep only the items you need, like users who are active.
• Don't use it to change the items themselves. Use Transformer for that.
• Don't use it to loop over a list. Use For Each Loop.

Inputs

Field	Required	Default	What it does
Operation	Yes	none	What to do, see the table below.
Datasource	Yes	none	The name of the variable that holds the list. It must already exist, for example saved with Set Variable.
Value	For push and unshift	none	The item to add. A plain value, an object, or a JS expression like js: input.id.
Use Param As Input	No	off	On: add the previous block's output as the item, instead of Value.
Filter Conditions	For filter	none	Rules that an item must pass to be kept. Built like If Condition rules, and each item is available as input.

Operation	What it does
push	Adds the item to the end of the list.
unshift	Adds the item to the beginning.
pop	Removes the last item.
shift	Removes the first item.
filter	Keeps only the items that pass the Filter Conditions.

Outputs

Handle	When it is used
Next (right)	Always. The next block receives the whole updated list.

Also, the Save output to variable option can store the updated list in outputs.<name>.

Example

Keep only the active users in a variable called users, which holds:

[{ "name": "Avery", "active": true }, { "name": "Kai", "active": false }]

Field	Value
Operation	filter
Datasource	users
Filter Conditions	One rule with operator JS: return input.active;

The variable users is now [{ "name": "Avery", "active": true }], and the next block receives that same list.

How it behaves

• The variable is changed in place. The list in the Datasource is updated, not just the output.
• Pop and shift return the list, not the removed item. To use the removed item, read it with JS Runner before you remove it.
• The Datasource must be a list. If the variable is missing or is not a list, the block fails with datasource is not an array and the Error Handler runs.
• Pop or shift on an empty list does nothing.
• No filter rules keeps everything. An empty condition list passes every item.
• Filter keeps the order of the items it keeps.

Related blocks

• Set Variable: create the list first, for example with the value js: [].
• For Each Loop: add something to a list on every round.
• Transformer: change the shape of each item.
• If Condition: the same rules, used to pick a path.