`tsc` with `--target ESNext` fails but the same configuration succeeds on the playground.

[scharf]

Bug Report

tsc causes errors for --target ESNext for some order of initialized variables and variables initialized in the constructor.

Why does the code produce errors for ESNext and no error for any other target?

🔎 Search Terms

• ESNext

🕗 Version & Regression Information

The command line fails on the code where the playground succeeds.

⏯ Playground Link

You have to set the --target to ESNext for this script Playground link with relevant code

💻 Code

Compiling this code with

./node_modules/.bin/tsc --target ESNext x.ts

function writeVal(a: number, b: any): number {
    console.log(‘writeVal’, a, b);
    return a;
}
class TestClass {
    a: number;
    public b = writeVal(2, this.z);    
    constructor(public z: number) {
        this.a = writeVal(1, this.z);
    }
    public c = writeVal(3, this.z);
}

I get the following error:

x.ts:7:33 - error TS2729: Property ‘z’ is used before its initialization.

7     public b = writeVal(2, this.z);
                                  ~

  x.ts:8:17
    8     constructor(public z: number) {
                      ~~~~~~~~~~~~~~~~
    ‘z’ is declared here.

x.ts:11:33 - error TS2729: Property ‘z’ is used before its initialization.

11     public c = writeVal(3, this.z);
                                   ~

  x.ts:8:17
    8     constructor(public z: number) {
                      ~~~~~~~~~~~~~~~~
    ‘z’ is declared here.

Found 2 errors.

🙁 Actual behavior

Running the code above in the playground there is no error, but tsc throws errors and fails to compile.

🙂 Expected behavior

Playground and the compiler should produce the same errors.

[scharf]

This is the las version where the code compiles successfully:

npm i typescript@4.3.0-dev.20210407

This is the first version when the code breaks:

npm i typescript@4.3.0-dev.20210408

[scharf]

It is broken up to version npm i typescript@4.4.0-dev.20210802

[MartinJohns]

I get the same error in the playground: https://www.typescriptlang.org/play?useDefineForClassFields=true&target=99&ts=4.4.0-beta#code/GYVwdgxgLglg9mABAdwE4ygUwGoEMA2AFLgFyJggC2ARpqgDSLVm5gCeAlGRTXYgN4AoRCMQQEAZzj5MAOnxwA5oQDkaDDgIrGuRtQ4BuYaNSYoIVElxGAvoIj5cEiYgAqmCVADCj5wOMipORUtKhGoogADiDU+DAQTIgAvCjoWHhEAEyMUAAWMBKyAF6GEQFiklCoINBwqITRsfGIRdwhdBz+ERF5BbK4yakaGYQAjDn5hSXhonYRjXEJCSnq6QSEAMwTfdOCNkA

Note that useDefineForClassFields is by default true when targeting ESNext, but it needs to separately enabled in the Playground.