title: Angular 2: disable button if there are changes in form
body: <p>I want to check if <em>at least one field in my form is changed</em>. If this scenario is true, the <code>disableButton</code> will be set to <strong>true</strong>, and <strong>false</strong> if there are <em>no changes</em> in the form. Below is my current code:</p>
  
  <pre><code>// this.hold is an array that temporary holds the previous values of 
  // the form for comparison of the changes in form
  
  if(this.data.process == 'update') {
     for(const f in form.value){
         if (form.value[f] == this.hold[f])
             this.disableButton = true;
         else
             this.disableButton = false;
     }
  }
  </code></pre>
  
  <p>The problem is, the button only disables when <strong>ALL</strong> fields are
  changed. What should I add in my condition or in for loop?</p>