Flow
A typed dialect of JavaScript with a static type system
Flow is a typed dialect of JavaScript that adds a static type system and first-class language constructs to the language. It is designed to catch errors at compile time, including cases that TypeScript may allow through, such as extra properties on objects or methods called without their required receiver.
Flow includes familiar TypeScript-compatible syntax such as keyof, readonly props, unknown, indexed access types, conditional types, mapped types, and type guards. It adds built-in React support through component and renders syntax, where props are named parameters typed inline with defaults, and only components that render a specified type can be passed to a renders prop. Flow also provides match, an exhaustively checked pattern-matching expression and statement that replaces switch without fall-through, and exact object types by default that reject extra properties at assignment.
Flow is available to try in the browser and can be used in existing projects, with guidance for TypeScript users. It is used in production at Meta across large JavaScript and React codebases.
11 alternatives to Flow
Ranked by how well each tool replaces Flow: shared features, audience, price and popularity.
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Covers 1 of 11 key features, has a free plan and is open source.
Free planOpen source58 out of 100 matchFreeA strongly typed programming language built on top of JavaScript
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56 out of 100 match—Dart: An approachable, portable, and productive language for high-quality apps on any pla
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Open source56 out of 100 match—BAML is Basically A Made-up Language, a programming language designed for AI agents.
Covers 1 of 11 key features, has a free plan and is open source.
Free planOpen source49 out of 100 matchContact salesA C language family frontend for LLVM.
Covers 1 of 11 key features and is open source.
Open source49 out of 100 match—Visualize, Analyze, and Understand Your Code flow. Turn Code into Interactive Flowcharts.
Covers 0 of 11 key features and has a free plan.
Free plan45 out of 100 match$9.99/mo- 45 out of 100 match$39/mo
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Covers 0 of 11 key features, has a free plan and is open source.
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Covers 0 of 11 key features.
38 out of 100 match—The self-hosted knowledge graph for enterprises.
Covers 1 of 11 key features, has a free plan and is open source.
Free planOpen source38 out of 100 match$29/moBuild industrial applications in minutes with AI, then deploy and govern production from
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Open source37 out of 100 matchContact sales