TypeScript to ArkTS Syntax Differences

This file highlights TypeScript patterns that often need rewriting in ArkTS.

Dynamic JavaScript patterns are narrower

• ArkTS is not a drop-in TypeScript superset in practice.
• Patterns that depend on dynamic object mutation, loose shape matching, or reflective syntax are often rejected.
• Patterns based on Record<string, T>, arbitrary indexes, or namespace objects often need explicit ArkTS models.

Reference:

• Guide: docs/ArkTS-Language-Guide/09-Migration-Guide/01-TypeScript-to-ArkTS/typescript-to-arkts-migration-guide.md
• Linter summary: overview section

Prefer named types over inline shapes

TypeScript style:

function printPoint(point: { x: number; y: number }): void {}

ArkTS style:

interface PointLike {
  x: number
  y: number
}

function printPoint(point: PointLike): void {}

Reference:

• Guide: docs/ArkTS-Language-Guide/02-Basic-Syntax/interfaces.md

Prefer declarations over expressions

• Rewrite function expressions to arrow functions when the function is used as a value.
• Rewrite class expressions to named class declarations.
• Move nested function declarations to top-level declarations, class methods, or arrow-function values.

Reference:

• Guide: docs/ArkTS-Language-Guide/02-Basic-Syntax/classes.md
• Linter summary: function and class sections

Prefer explicit class and interface modeling

• TypeScript often treats classes as object shapes; ArkTS prefers constructor-based initialization and declared members.
• TypeScript often relies on structural typing; ArkTS narrows that style and expects explicit named contracts.
• TypeScript often uses Record or indexed access for flexible maps; ArkTS authoring should prefer named interfaces/classes and direct property access when property names are known.

Reference:

• Guide: docs/ArkTS-Language-Guide/02-Basic-Syntax/classes.md
• Guide: docs/ArkTS-Language-Guide/02-Basic-Syntax/interfaces.md
• Linter summary: structural typing restriction

Rewrite template strings

TypeScript style:

const label: string = `Count: ${count}`

ArkTS style:

const label: string = "Count: " + count.toString()

Reference:

• Linter summary: syntax restriction section

Rewrite namespace-as-value patterns

TypeScript style:

const api = common
api.doWork()

ArkTS style:

common.doWork()

If the code needs a runtime object, define that object explicitly instead of using a namespace as the value.

Reference:

• Linter summary: namespace section

Remove unsupported or narrowed syntax

Common rewrites:

• var -> let or const
• destructuring declaration -> explicit local bindings
• value as T -> typed variable, typed function return, constructor, or explicit conversion
• `${value}` -> string concatenation with explicit conversion
• delete obj.x -> construct the desired value without runtime property deletion
• catch (err: Error) -> catch (err)
• type T = typeof Foo -> use the explicit type you need instead of a type query

Reference:

• Linter summary: declaration, operator, and statement sections