Reactive form key value pair bootstrap & angular 4-5-6-7.

<div class="container">
  <form [formGroup]="keyValueForm" (ngSubmit)="doSubmit()">
    <div class="form-row" formArrayName="details" *ngFor="let field of keyValueForm.get('details').controls; let ind = index;">
      <ng-container [formGroupName]="ind">
        <div class="form-group col-md-5">
          <label>Key</label>
          <input type="email" class="form-control" formControlName="key" placeholder="Key">
        </div>
        <div class="form-group col-md-5">
          <label>Value</label>
          <input type="text" class="form-control" formControlName="value" placeholder="Value">
        </div>
        <div class="form-group col-md-2" *ngIf="ind > 0">
          <button class="btn btn-danger" (click)="removeRow(ind)" style="margin-top:30px;">Remove</button>
        </div>
      </ng-container>
    </div>
  </form>

  <button class="btn btn-success" (click)="addRow()">Add Row</button>
</div>
<pre>
  {{keyValueForm.value | json}}
</pre>

import { Component } from '@angular/core';
import { FormBuilder, FormGroup, Validators, FormControl, FormArray } from '@angular/forms';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  public keyValueForm: FormGroup;
  constructor(private formBuilder: FormBuilder) {
    const items = [];
    items.push(this.formBuilder.group({
      key: new FormControl(''),
      value: new FormControl('')
    }));

    items.push(this.formBuilder.group({
      key: new FormControl(''),
      value: new FormControl('')
    }));

    this.keyValueForm = this.formBuilder.group({
      details: this.formBuilder.array(items)
    });
  }

  addRow() {
    const details = this.keyValueForm.get('details') as FormArray;
    details.push(this.createItem());
  }

  removeRow(index) {
    const details = this.keyValueForm.get('details') as FormArray;
    details.removeAt(index);
  }

  createItem(): FormGroup {
    return this.formBuilder.group({
      key: [],
      value: []
    });
  }
}