title: TypeError: obj[key].includes is not a function when filtering values of an object in an array
body: <p>I wanted to filter the values in an array of objects by a certain value. When I run the function, I get <code>TypeError: obj[key].includes is not a function</code>. I am using reactjs. What I'm I missing in the function?</p>
  
  <pre><code>var arr = [{
   name: 'xyz',
   grade: 'x'
  }, {
   name: 'yaya',
   grade: 'x'
  }, {
   name: 'x',
   frade: 'd'
  }, {
    name: 'a',
    grade: 'b'
  }];
  
  filterIt(arr, searchKey) {
    return arr.filter(obj =&gt; Object.keys(obj)
      .map(key =&gt; obj[key].includes(searchKey)));
  }
  </code></pre>
  
  <p>I got this example from <a href="https://stackoverflow.com/a/40890687/5256509">https://stackoverflow.com/a/40890687/5256509</a> and tried it out</p>