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TypeScript · 17 Editing Models with Utility Types

Series contents · Technology map

Stage: Validation and Type Transformations · Editable example · Storage ID: typescript-step-17

Goals and learning outcomes

Prerequisites

Work and experiment records from Unit 16, “Passing Failures with Result Types”

Key concepts and explanations

Derived Models

Pick and Omit create new contracts from some properties of an existing type. They do not automatically remove properties from runtime objects.

Partial Updates

Partial makes all properties optional. Decide first whether id should also be editable.

Practice setup

First check the execution scope guidance on the example screen. The following environment is for extending the assignment in a separate project. Implement it yourself in a separate local project and check it with browser developer tools and tsc --noEmit. 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 patch.ts, prepare conditions for a title-only update, a completion-only update, and an attempted id change.
  2. Create an editing type excluding id and a read-summary type, then implement applyPatch.
  3. Run with a title-only update, a completion-only update, and an attempted id change. Results to check: Both valid patches preserve the existing id. Record the compiler error for an id patch. Record expected and actual results separately.

Variables to observe

VariableBaselineChangeExpected change / hypothesis
Patch KeytitleidPre-run hypothesis: the non-editable field will be rejected. Keep other conditions fixed and record the actual result separately after running.

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

Completion criteria

Self-check

  1. Does Omit delete fields from JSON?
  2. Can Partial alone prevent an empty patch?

Official references

Linked example and execution scope

Example source · Runtime environments and limits

The preview is a JavaScript runtime boundary experiment. It does not run TypeScript diagnostics. Check lesson.ts locally with tsc --strict --noEmit --lib ES2023,DOM.

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

Next learning

Previous: Passing Failures with Result Types · Next: Checking Configuration with satisfies

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