TS2802: Type can only be iterated through when using the '--downlevelIteration' flag TypeScript Origin: On your device OSI layer 7 · Application Last updated 5 Nov 2026

TypeScript: error TS2802: Type 'Set<string>' can only be iterated through when using the '--downlevelIteration' flag or with a '--target' of 'es2015' or higher

You iterate a Set/Map/generator with an old compile target (ES5) where for...of/spread aren't natively supported.

Exact message you may see error TS2802: Type 'Set<string>' can only be iterated through when using the '--downlevelIteration' flag or with a '--target' of 'es2015' or higher.can only be iterated through when using the '--downlevelIteration' flagTS2802 downlevelIterationTS2569: Type 'Map<string, number>' is not an array type or a string type. Use compiler option '--downlevelIteration' to allow iterating of iterators.
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Seen on: TypeScript

Meaning

Set "target": "es2015" (or higher, ideally es2020+), or enable downlevelIteration: true. Modern setups should target ES2020/ES2022; check lib includes es2015+.

Common causes

  • target: "es5"
  • Old tsconfig templates
  • lib missing es2015+
  • Spread of Set/Map/iterators
  • for...of over iterables

⚡ Quick fix

  1. "target": "ES2020" in tsconfig
  2. Or "downlevelIteration": true
  3. Ensure "lib": ["ES2020", "DOM"]

Detailed fix by platform

TypeScript

  1. { "compilerOptions": { "target": "ES2020", "lib": ["ES2020", "DOM"] } }

How to diagnose

  1. target — ES5?
  2. lib — es2015+?
  3. Flag — downlevelIteration?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: On your device. Errors that are often confused with or caused by this one (click to open):

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