@Type(() => Date) breaks custom @Transform for classToPlain

Author: ehaynes99Created Sep 3, 2021Updated Mar 31, 2026

Labelstype: fixstatus: needs triage

Description

When using @Type(() => Date) along with an @Transform, calling plainToClass appears to first run the custom transform, then convert that result back into a Date.

typescript

class Example {
  @Type(() => Date)
  @Transform(() => '2222-12-31', { toPlainOnly: true })
  timestamp!: Date;
}

const instance = plainToClass(Example, { timestamp: '2021-01-01' });
const t1 = instance.timestamp;
const t2 = classToPlain(instance).timestamp;

console.log('instance', t1, typeof t1, 'is date:', t1 instanceof Date);
console.log('plain obj', t2, typeof t2, 'is date:', t2 instanceof Date);

Expected behavior

instance 2021-01-01T00:00:00.000Z object is date: true
plain obj 2222-12-31 string is date: false

Actual behavior

instance 2021-01-01T00:00:00.000Z object is date: true
plain obj 2222-12-31T00:00:00.000Z object is date: true

This seems to be specific to Date, as doing similar with @Type(() => Number) does not exhibit this behavior.

Source: typestack/class-transformer

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