What is !== in javascript?
<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>
