title: Adding custom functions to javascript's Array class breaks array declaration
body: <p>One of my Nodejs project I've added a solution from stackoverflow for finding differences between two arrays.</p>
  <pre><code>Array.prototype.diff = function (arr2) {
      return this.filter((x) =&gt; !arr2.includes(x));
  };
  </code></pre>
  <p>Until today, everything was working fine but today my personal cli got broken without any reason and I realized that, on array declaration nodejs automatically adds key value pair to array. (key:diff, value:function (arr2)...)</p>
  <pre><code>    const values = [];
      for (const i in values) {
          console.log(i, values[i]);
      }
      // diff [Function (anonymous)]
  
  </code></pre>
  <p>I've removed the function from other project, upgraded nodejs to higher version but it still adds above key value pair. How can I fix this?</p>