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TypeScript for Beginners: Catch Wrong Data Before It Runs
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TypeScript for Beginners: Catch Wrong Data Before It Runs

Check Yourself: Compile Without the Mystery

Five scenario questions on tsconfig settings and reading errors. If you miss more than one, go back to the two lessons before moving on.

5 min TypeScriptProgramming BasicsTesting and DebuggingType Systems Beginner
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1. You ran tsc --init, and now npx tsc hello.ts prints error TS5112 about tsconfig.json. What is the cleanest way to continue?
Rename hello.ts to hello.js. Delete node_modules and reinstall TypeScript. Turn strict off. Run npx tsc without a file name so it compiles the project, or pass --ignoreConfig if you really want the single file.
2. With target es2015 the output turns a ?? b into a longer older form, and with target es2022 it stays as ?? . What does target control?
How many errors the compiler reports. Which files are included in the project. Which JavaScript version the output is written in, so newer syntax is rewritten for older engines. Whether imports become require calls or import statements.
3. You want tsc to write no JavaScript at all while the project has errors. Which setting does that?
outDir set to an empty folder. noEmitOnError set to true in compilerOptions. strict set to true. target set to esnext.
4. A long error ends with the line Property city is missing in type with name only but required in type Customer. The first line says an object is not assignable to Order. How should you read it?
Only the first line matters. Fix the first line by casting the object to Order. The first line says where it does not fit, and the last line says why. Ignore it, because a long message means a compiler bug.
5. A function has no return type and returns a number in one case and a string in the other. The error appears on a line that multiplies its result. Where is the real mistake?
In the multiplication, which should use a different operator. In tsconfig.json, which needs strict turned off. In the function above, which returns two kinds of value. A declared return type would move the error to the wrong return line. Nowhere, because the compiler guessed wrong.

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Five scenario questions on tsconfig settings and reading errors. If you miss more than one, go back to the two lessons before moving on.

Duration
5 min
Last update
10/11/2026
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