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$ curl repovive.com/roadmaps/javascript/introduction-to-typescript/type-narrowing

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$ curl repovive.com/roadmaps/javascript/introduction-to-typescript/type-narrowing

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Type Narrowing - Introduction to TypeScript | JavaScript | Repovive

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JavaScript22 sections · 783 units18h total

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Type Narrowing

Refine types with conditions

TypeScript narrows types inside conditional blocks:

function process(value: string | number) {
  if (typeof value === "string") {
    // TypeScript knows value is string here
    console.log(value.toUpperCase());
  } else {
    // TypeScript knows value is number here
    console.log(value.toFixed(2));
  }
}

TypeScript tracks the possible types through your code.