Remove all items from a FormArray in Angular

Question

I have a form array inside a FormBuilder and I am dynamically changing forms  i e  on click load data from application 1 etc  The issue I am having is that all the data loads in but the data in the FormArray stays and just concats the old items with new  How do I clear that FormArray to only have the new items  I ve tried this const control2    lt FormArray gt this registerForm controls  other Partners    control2 setValue       but it doesn t work  Any ideas  ngOnInit    void     this route params subscribe params   gt        if  params  id            this id   Number parseInt params  id           else   this id   null           if  this id    null  amp  amp  this id    NaN        alert this id       this editApplication        this getApplication this id       else       this newApplication           onSelect Editedapplication  Application      this router navigate    apply   Editedapplication id       editApplication       this registerForm   this formBuilder group       id  null      type of proposal       Validators required       title        Validators required  Validators minLength 5         lead teaching fellow        Validators required  Validators minLength 5         description        Validators required  Validators minLength 5         status          userID  JSON parse localStorage getItem  currentUser    username      contactEmail  JSON parse localStorage getItem  currentUser    email      forename  JSON parse localStorage getItem  currentUser    firstname      surname  JSON parse localStorage getItem  currentUser    surname      line manager discussion  true      document url          keywords        Validators required  Validators minLength 5         financial Details  this formBuilder group         id  null        buying expertise description        Validators required  Validators minLength 2           buying expertise cost        Validators required          buying out teaching fellow cost        Validators required          buying out teaching fellow desc        Validators required  Validators minLength 2           travel desc        Validators required  Validators minLength 2           travel cost        Validators required          conference details desc        Validators required  Validators minLength 2           conference details cost        Validators required                 partners  this formBuilder array             this initEditPartner              this initEditPartner              this initMultiplePartners 1                     other Partners  this formBuilder array           this initEditOther Partners                    getApplication id      this applicationService getAppById id  JSON parse localStorage getItem  currentUser    username       subscribe Response   gt          if  Response json      false            this router navigateByUrl               else           this application   Response json            for  var i   0  i  lt  this application partners length i                this addPartner                      for  var i   0  i  lt  this application other Partners length  i                this addOther Partner                       this getDisabledStatus Response json   status             lt FormGroup gt this registerForm   setValue Response json      onlySelf  true                        ngOnInit is not being called on click

User · Answer

To keep the code clean I have created the following extension method for anyone using Angular 7 and below  This can also be used to extend any other functionality of Reactive Forms   import   FormArray   from   angular forms    declare module   angular forms src model      interface FormArray       clearArray       gt  FormArray         FormArray prototype clearArray   function        const  self   this as FormArray     self controls          self setValue         self updateValueAndValidity      return  self

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Or you can simply clear the controls this myForm         name  new FormControl  quot  quot         desc  new FormControl  quot  quot         arr  new FormArray        Add something array const arr    lt FormArray gt this myForm controls arr  arr push new FormControl  quot X quot      Clear the array const arr    lt FormArray gt this myForm controls arr  arr controls        When you have multiple choices selected and clear  sometimes it doesn t update the view  A workaround is to add arr removeAt 0   UPDATE A more elegant solution to use form arrays is using a getter at the top of your class and then you can access it  get inFormArray    FormArray       this myForm get  inFormArray   as FormArray     And to use it in a template  lt div  ngFor  quot let c of inFormArray  let i   index  quot   formGroup   quot i quot  gt  other tags     lt  div gt   Reset  inFormArray reset     Push  inFormArray push new FormGroup        Remove value at index  1 inFormArray removeAt 1    UPDATE 2  Get partial object  get all errors as JSON and many other features  use the NaoFormsModule

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Update  Angular 8 finally got method to clear the Array FormArray clear

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You can easily define a getter for your array and clear it as follows     formGroup  FormGroup       constructor private fb  FormBuilder         ngOnInit         this formGroup   this fb group         sliders  this fb array                  get sliderForms         return this formGroup get  sliders   as FormArray        clearAll         this formGroup reset       this sliderForms clear

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As of Angular 8  you can use clear   to remove all controls in the FormArray   const arr   new FormArray      new FormControl       new FormControl       console log arr length       2  arr clear    console log arr length       0   For previous versions the recommended way is   while  arr length       arr removeAt 0       https   angular io api forms FormArray clear

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Angular v4 4 if you need to save the same reference to the instance of FormArray try this   purgeForm form  FormArray      while  0     form length        form removeAt 0

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If you are using Angular 7 or a previous version and you dont  have access to the clear   method  there is a way to achieve that without doing any loop  yourFormGroup controls youFormArrayName   new FormArray

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Use FormArray clear   to remove all the elements of an array in a FormArray

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I never tried using formArray  I have always worked with FormGroup  and you can remove all controls using   Object keys this formGroup controls  forEach key   gt              this formGroup removeControl key                 being formGroup an instance of FormGroup

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I had same problem  There are two ways to solve this issue   Preserve subscription  You can manually clear each FormArray element by calling the removeAt i  function in a loop    clearFormArray    formArray  FormArray    gt      while  formArray length     0        formArray removeAt 0             The advantage to this approach is that any subscriptions on your formArray  such as that registered with formArray valueChanges  will not be lost    See the FormArray documentation for more information     Cleaner method  but breaks subscription references   You can replace whole FormArray with a new one   clearFormArray    formArray  FormArray    gt      formArray   this formBuilder array             This approach causes an issue if you re subscribed to the formArray valueChanges observable  If you replace the FromArray with a new array  you will lose the reference to the observable that you re subscribed to

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I am very late but I found some other way where you don t need to have loops  you can reset array by setting array control to empty   Below code will reset your array   this form setControl  name   this fb array

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Angular 8  simply use clear   method on formArrays     this invoiceForm controls  other Partners   as FormArray  clear

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Since Angular 8 you can use this formArray clear   to clear all values in form array  It s a simpler and more efficient alternative to removing all elements one by one

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Provided the data structure for what you will be replacing the information in the array with matches what is already there you can use patchValue  https   angular io docs ts latest api forms index FormArray-class html   reset-anchor     patchValue value  any     onlySelf  emitEvent     onlySelf   boolean    emitEvent   boolean     void Patches the value of the FormArray  It   accepts an array that matches the structure of the control  and will   do its best to match the values to the correct controls in the group       It accepts both super-sets and sub-sets of the array without throwing   an error    const arr   new FormArray      new FormControl       new FormControl       console log arr value         null  null  arr patchValue   Nancy     console log arr value          Nancy   null    Alternatively you could use reset     reset value   any   onlySelf  emitEvent     onlySelf   boolean    emitEvent   boolean     void Resets the FormArray  This means by   default       The array and all descendants are marked pristine The array and all   descendants are marked untouched The value of all descendants will be   null or null maps You can also reset to a specific form state by   passing in an array of states that matches the structure of the   control  The state can be a standalone value or a form state object   with both a value and a disabled status    this arr reset   name    last name     console log this arr value         name    last name        OR   this arr reset      value   name   disabled  true      last      console log this arr value         name    last name   console log this arr get 0  status        DISABLED    Here s a forked Plunker demo from some earlier work of mine demoing a very simple utilization of each

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While loop will take long time to delete all items if array has 100 s of items  You can empty both controls and value properties of FormArray like below   clearFormArray    formArray  FormArray       formArray controls       formArray setValue

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Warning   The Angular v6 1 7 FormArray documentation says      To change the controls in the array  use the push  insert  or removeAt   methods in FormArray itself  These methods ensure the controls are   properly tracked in the form s hierarchy  Do not modify the array of   AbstractControls used to instantiate the FormArray directly  as that   result in strange and unexpected behavior such as broken change   detection    Keep this in mind if you are using the splice function directly on the controls array as one of the answer suggested   Use the removeAt function     while  formArray length     0        formArray removeAt 0

[angular] Remove all items from a FormArray in Angular

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