title: Disable Reactive Form's Input Fields
body: <p><a href="https://i.stack.imgur.com/xNgtI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xNgtI.png" alt="enter image description here" /></a></p>
  <p>The image shows how my form fields appears. I want to know what is the best way to disabled rest form input fields when user type in 'Discount Percentage' and its relevant 'Remark'.</p>
  <p>Ex 1:- If user type in Discount Percentage field then Discount Amount, Additional Loading Percentage and Additional Loading amount and their relevant Remark fields will be Disabled.</p>
  <p>Ex 2:- If user type in Additional Loading Amount field then Discount Amount, Additional Loading Percentage and Discount Percentage and their relevant Remark fields will be Disabled.</p>
  <p>If user clear the input field then disabled input fields should be enabled again.</p>
  <pre><code>    formGroup = new FormGroup({
          discountPercentage: new FormControl(),
          discountPercentageRemark: new FormControl(''),
          discountAmount: new FormControl(),
          discountAmountRemark: new FormControl(''),
          loadingPercentage: new FormControl(),
          loadingPercentageRemark: new FormControl(''),
          loadingAmount: new FormControl(),
          loadingAmountRemark: new FormControl('')
    })
  </code></pre>