title: What is !== in javascript?
body: <p><strong>The code is used to verify an image or cell selection. My question is
  What is !== used for in the following function:</strong></p>
  
  <pre><code>function checkSelected() {
      var cellList,
          selectedCell,
          imgList,
          selectedImg,
          i
  
      cellList = document.getElementById("imgTable")
      cellList = cellList.getElementsByTagName("td")
  
      imgList = document.getElementById("b_list")
      imgList = imgList.getElementsByTagName("img")
  
      if (cellList[0].style.border.indexOf("7px outset") !== -1) { selectedCell = cellList[0] }
  
  
      if (selectedCell === undefined || selectedImg === undefined) { return }
  
      selectedCell.style.backgroundImage = "url(" + selectedImg.src + ")"
      selectedCell.firstChild.style.visibility = "hidden"
  
      selectedCell.style.border = "1px solid"
      selectedImg.style.border = "1px solid"
  }
  </code></pre>