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TypeScript · 24 Modules and type-only import

Series contents · Technology map

Stage: Module Contracts and Plugins · Editable example · Storage ID: typescript-step-24

Goals and learning outcomes

Record differences in emitted code for type-only import.
Load the modules in the actual environment and check for errors.

Prerequisites

Work and experiment records from Unit 23, “Async Functions and Error Types”

Key concepts and explanations

Importing Types

import type explicitly marks a type-only use. This distinguishes it from runtime dependencies.

Execution Environment

module and moduleResolution must match the execution and bundling environment. Changing options alone does not automatically resolve path issues.

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

In contracts.ts, prepare conditions for two modules in a browser bundling environment.
Export a type and read it with import type in main.ts, then compare emitted output with an actual function import.
Run with two modules in a browser bundling environment. Results to check: Record differences in emitted code for type-only import. Load the modules in the actual environment and check for errors. Record expected and actual results separately.

Variables to observe

Variable	Baseline	Change	Expected change / hypothesis
Import Kind	ordinary value import	import type	Pre-run hypothesis: the type-only dependency will be removed from executable code. 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

Record differences in emitted code for type-only import.
Load the modules in the actual environment and check for errors.

Self-check

Can a type-only import be used as a value?
Why might module loading fail after successful compilation?

Official references

TypeScript Handbook

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: Async Functions and Error Types · Next: Declaration Files and External Boundaries

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