Angular Reactive forms : how to get just changed values

Question

Im building a reactive forms using angular 6, this form contain 3 attributes (name,age,phone) and i would to get just the changed values not all form values.

this.refClientForm = this.formBuilder.group({
  name: [],
  phone: [],
  age: []
});

for the form listener :

 this.refClientForm.valueChanges.subscribe(values => console.log(values))

but i got always all form values.

Possible duplicate of [Angular 2 getting only the dirty values in a controlgroup](https://stackoverflow.com/questions/37342444/angular-2-getting-only-the-dirty-values-in-a-controlgroup) — JayChase, Jun 05 '19 at 02:45

score 23 · Accepted Answer · edited Dec 04 '18 at 14:19

23

You can check all controls for dirty-flag. See https://angular.io/api/forms/FormControl

getDirtyValues(form: any) {
        let dirtyValues = {};

        Object.keys(form.controls)
            .forEach(key => {
                let currentControl = form.controls[key];

                if (currentControl.dirty) {
                    if (currentControl.controls)
                        dirtyValues[key] = this.getDirtyValues(currentControl);
                    else
                        dirtyValues[key] = currentControl.value;
                }
            });

        return dirtyValues;
}

edited Dec 04 '18 at 14:19

AHmedRef

2,555
12
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75

answered Dec 04 '18 at 13:16

J. Knabenschuh

747
4
15

controls object is not a array – AHmedRef Dec 04 '18 at 13:21
Yeah you are right. I updated the post. But the idea is the same. Of course you could also loop over the controls obejcts via `for in` or something like then you also get the name. – J. Knabenschuh Dec 04 '18 at 13:22
Duplicate to https://stackoverflow.com/questions/37342444/angular-2-getting-only-the-dirty-values-in-a-controlgroup – J. Knabenschuh Dec 04 '18 at 13:26

score 5 · Answer 2 · answered Jun 29 '21 at 15:31

5

Better answer found here:

Angular 2 Reactive Forms only get the value from the changed control

this.imagSub = this.imagingForm.valueChanges.pipe(
    pairwise(),
    map(([oldState, newState]) => {
      let changes = {};
      for (const key in newState) {
        if (oldState[key] !== newState[key] && 
            oldState[key] !== undefined) {
          changes[key] = newState[key];
        }
      }
      return changes;
    }),
    filter(changes => Object.keys(changes).length !== 0 && !this.imagingForm.invalid)
  ).subscribe(
    value => {
      console.log("Form has changed:", value);
    }
  );

answered Jun 29 '21 at 15:31

ktamlyn

4,519
2
30
41

This was what I needed, as I just want the "latest" changed value instead of "all" changed values. I also like the rxJs utilities used for this. – Justus Romijn Mar 30 '23 at 08:29
With this answer, the code inside subscribe is not executed for the the very first value change – Rivosoa Jun 15 '23 at 08:55

score 1 · Answer 3 · answered Mar 20 '19 at 14:06

1

There is a simple way to check if any control is dirty in the reactive form.

getUpdatedValues() {
 const updatedFormValues = {};
 this.form['_forEachChild']((control, name) => {
  if (control.dirty) {
      this.updatedFormValues[name] = control.value;
  }
});
console.log(this.updatedFormValues);

answered Mar 20 '19 at 14:06

bhavik shah

744
7
11

4

Not good practice to use `_forEachChild`, the other answer is correct. – ktamlyn Jun 29 '21 at 15:18

score -1 · Answer 4 · answered Nov 26 '21 at 07:55

-1

use pairwise() operator with startWith(this.refClientForm.value) operator then form valueChanges will emit on first try

answered Nov 26 '21 at 07:55

Sayax

1

2

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Nov 26 '21 at 10:09

Angular Reactive forms : how to get just changed values

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