JS - Element properties

It returns a collection of attributes in an element, i.e. a NamedNodeMap : an array-like unordered collection of an element's attributes or a list of Attr objects.
Its "length" property returns the number of nodes, which can be accessed by name or index numbers. The index starts at 0.

code:

                <div>
                    <img id="myImg" alt="holiday" src="../../pics/1.jpg" width="150" height="113">
                    <p id="prop3"></p>
                    <p id="prop4"></p>
                </div>
                <script>
                    let num = document.getElementById("myImg").attributes.length;
                    document.getElementById("prop3").innerHTML = "NameNodeMap : " + num;
                    const nodeMap = document.getElementById("myImg").attributes;
                    let text = "";
                    for (let i = 0; i < nodeMap.length; i++) {
                        text += nodeMap[i].name + " = " + nodeMap[i].value + "<br>";
                    }
                    document.getElementById("prop4").innerHTML = text;
                </script>

Click "try it" to display the numer of button attributes:

            <div>
                <p>Click "try it" to display the numer of button attributes:</p>
                <button id="myButton" onclick="firstFunction()">Try it</button>
                <p id="demo"></p>
            </div>
            <script>
                function firstFunction() {
                    let numb = document.getElementById("myButton").attributes.length;
                    document.getElementById("demo").innerHTML = numb;
                }
            </script

JS - element properties - attributes

returns a NamedNodeMap of an element's attributes.