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# Operator reference

Declarative expressions (`$expression`) admit a closed set of operators, enforced by the Jx schema. This page enumerates that set straight from `packages/schema/schema.json`. The expression model itself is documented in the [Framework concepts](/docs/framework) section; named-formula composition is cataloged in the [formula catalog](/docs/framework/reference/formulas).

## Unary operators

Applied to a single `target` operand.

`!` · `-`

## Binary operators

Applied to a `target` and a `value` operand. Arithmetic, comparison, logical, and nullish-coalescing forms — the blessed subset of JavaScript's operator set (spec §19.4).

`+` · `-` · `*` · `/` · `%` · `===` · `!==` · `<` · `<=` · `>` · `>=` · `&&` · `||` · `??`

## Assignment operators

Statement-position only: assign (or read-modify-write) a state path. Not valid inside pure expressions.

`=` · `+=` · `-=` · `*=` · `/=`

## Conditional, switch, and call

`?:` selects between `value` and `else` on a `target` condition; `switch` matches a `target` against `cases`; `call` invokes a named formula (spec §19.4c) with `args`.

`?:` · `switch` · `call`

## Pure standard-library methods

Genuine pure `String`/`Array`/`Number` prototype methods, usable inside pure expressions (spec §19.4d). The change-by-copy family (`toSorted`, `toReversed`, `toSpliced`, `with`) replaces their mutating counterparts.

`includes` · `indexOf` · `lastIndexOf` · `join` · `slice` · `concat` · `at` · `flat` · `toSorted` · `toReversed` · `toSpliced` · `with` · `toUpperCase` · `toLowerCase` · `trim` · `trimStart` · `trimEnd` · `split` · `startsWith` · `endsWith` · `padStart` · `padEnd` · `replaceAll` · `repeat` · `charAt` · `normalize` · `toLocaleUpperCase` · `toLocaleLowerCase` · `toFixed` · `toPrecision` · `toLocaleString`

## Mutation methods

Statement-position array mutations. `pop`/`shift` take no argument; `push`/`unshift` take one; `splice` takes `start`, `deleteCount`, and `items`.

`pop` · `shift` · `push` · `unshift` · `splice`

## Iteration methods

`map`/`filter` evaluate their `value` expression per item with `$map/item` and `$map/index` in scope; `reduce` additionally exposes `$reduce/acc` and takes an `initial` value.

`reduce` · `map` · `filter`

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