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TypeScript · 14 Generics and Boundary Validation

Series contents · Technology map

Stage: Unions and Generics · Editable example · Storage ID: typescript-02

Goals and learning outcomes

• Record acceptance or rejection for all four inputs.
• Use Note fields on a valid return value without assertions.

Prerequisites

Work and experiment records from Unit 13, “Constraints and Minimal Contracts”

Key concepts and explanations

Storage Relationships

Type parameters express the type relationship between saving and loading. Stored strings must be validated again when loaded.

Structural Checks

Receive JSON.parse results as unknown and check them with a guard. Check null and fields inside arrays before trusting them.

Practice setup

The existing Frontory preview is a limited starting example, not a complete implementation of the assignment. Implement additional files and features yourself in a separate local project. Record the installed tsc version in a separate TypeScript project. Enable strict in tsconfig.json and check with tsc --noEmit, then open the runtime exercise using compiled output or a local development server. Do not assume the browser executes TS type annotations directly.

The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.

Practice tasks

1. In storage-boundary.ts, prepare conditions for a valid array, an empty array, null, and a numeric title.
2. Create save and load that accepts a validation function, then connect a Note array guard.
3. Run with a valid array, an empty array, null, and a numeric title. Results to check: Record acceptance or rejection for all four inputs. Use Note fields on a valid return value without assertions. Record expected and actual results separately.

Variables to observe

Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.

Completion criteria

• Record acceptance or rejection for all four inputs.
• Use Note fields on a valid return value without assertions.

Self-check

1. Does generic T check JSON structure?
2. Is an empty array valid under the contract?

Official references

• TypeScript Handbook
• TypeScript Generics

Linked example and execution scope

Example source · Runtime environments and limits

Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.

Next learning

Previous: Constraints and Minimal Contracts · Next: Type Guards and False Guarantees

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