🔎 Search Terms

• class
• constructor parameter
• useDefineForClassFields
• initialization

📌 Related issues

• Inconsistent parameter properties initialization order depending on the target syntax with useDefineForClassFields #45995
• Incorrect emit for parameter properties when using standard class fields #55132

🕗 Version & Regression Information

• This changed between versions ______ and _______
• This changed in commit or PR _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
• I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play/?useDefineForClassFields=true&target=7#code/PTAEAEBcEMCcHMCmkBcpEGcBMAGXAoECAVw0QBFEAzASwDtEAxAe1gGEAbaDDRmxDgBMMaSLGKJ8AYy49QAFQCeAB0QBlKbBrLIABTjQAtskSxdsZqtiR+GUAG98oZ6CJQMAWhrw6rSS9AqZmZQAF5QSAALGgwAOgAjOABuJxcpZjoMMWIpSFYACmVieI4aKVBE2DRoOkUASgdUgOd0zOYORFiOZnh8gCJaOmgODkU+gBoI6Lig5jqUgIBffGX8BgB3BRV1TW09A2NIU3NLUxtMfoA3YYk++aA

💻 Code

// @target: es2020
// @useDefineForClassFields: true
class TypeScriptParameterProperties {
    // @ts-ignore
    foo = this.bar;
    constructor(public bar: any) {
        console.log("finally", this.foo);
    }
}

new TypeScriptParameterProperties("value");

// @target: esnext
// @useDefineForClassFields: true
class TypeScriptParameterProperties {
    // @ts-ignore
    foo = this.bar;
    constructor(public bar: any) {
        console.log("finally", this.foo);
    }
}

new TypeScriptParameterProperties("value");

🙁 Actual behavior

Different compilation options will output different values.

es2020: "finally", "value"
esnext: "finally", undefined

🙂 Expected behavior

They should output the same value.

Additional information about the issue

• Can SWC match TS emit for Parameter Properties? swc-project/swc#9418
• fix(es/compat): Handle useDefineForClassFields: false swc-project/swc#7055 (comment)