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How do I solve this “Cannot read property 'appendChild' of null” error?

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既然无缘
既然无缘 2021-02-05 09:46

I tried to use this code below, which adds buttons in slideshow on my site:

window.onload = function loadContIcons() {
    var elem = document.createElement(\"im
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  • 醉酒成梦
    2021-02-05 10:21

    The element hasn't been appended yet, therefore it is equal to null. The Id will never = 0. When you call getElementById(id), it is null since it is not a part of the dom yet unless your static id is already on the DOM. Do a call through the console to see what it returns.

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  • 春和景丽
    2021-02-05 10:25

    For all those facing a similar issue, I came across this same issue when i was trying to run a particular code snippet, shown below.

    <html>
    <head>
        <script>
                var div, container = document.getElementById("container")
                for(var i=0;i<5;i++){
                    div = document.createElement("div");
                    div.onclick = function() { 
                        alert("This is a box #"+i);
                    };
                    container.appendChild(div);
                }
            </script>

    </head>
    <body>
        <div id="container"></div>
    </body>
 </html>

    https://codepen.io/pcwanderer/pen/MMEREr

    Looking at the error in the console for the above code.

    Since the document.getElementById is returning a null and as null does not have a attribute named appendChild, therefore a error is thrown. To solve the issue see the code below.

    <html>
    <head>
        <style>
        #container{
            height: 200px;
            width: 700px;
            background-color: red;
            margin: 10px;
        }


        div{
            height: 100px;
            width: 100px;
            background-color: purple;
            margin: 20px;
            display: inline-block;
        }
        </style>
    </head>
    <body>
        <div id="container"></div>
        <script>
                var div, container = document.getElementById("container")
                for(let i=0;i<5;i++){
                    div = document.createElement("div");
                    div.onclick = function() { 
                        alert("This is a box #"+i);
                    };
                    container.appendChild(div);
                }
            </script>
    </body>
</html>

    https://codepen.io/pcwanderer/pen/pXWBQL

    I hope this helps. :)

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  • 无人及你
    2021-02-05 10:31

    Your condition id !== 0 will always be different that zero because you are assigning a string value. On pages where the element with id views_slideshow_controls_text_next_slideshow-block is not found, you will still try to append the img element, which causes the Cannot read property 'appendChild' of null error.

    Instead of assigning a string value, you can assign the DOM element and verify if it exists within the page.

    window.onload = function loadContIcons() {
    var elem = document.createElement("img");
    elem.src = "http://arno.agnian.com/sites/all/themes/agnian/images/up.png";
    elem.setAttribute("class", "up_icon");

    var container = document.getElementById("views_slideshow_controls_text_next_slideshow-block");
    if (container !== null) {
        container.appendChild(elem);
    } else console.log("aaaaa");

    var elem1 = document.createElement("img");
    elem1.src = "http://arno.agnian.com/sites/all/themes/agnian/images/down.png";
    elem1.setAttribute("class", "down_icon");

    container = document.getElementById("views_slideshow_controls_text_previous_slideshow-block");
    if (container !== null) {
        container.appendChild(elem1);
    } else console.log("aaaaa");
}
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  • 别那么骄傲
    2021-02-05 10:35

    Just reorder or make sure, the (DOM or HTML) is loaded before the JavaScript.

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