javascript - Dynamically Populating Drop down list from selection of another drop down value

Question

My requirement is that for a selection in a 'meal' drop down list, a second drop down list 'category' should get dynamically populated with values related to the selection in first drop down list. Then depending on what is selected in the meal dropdown, the list should change in category. I have written the following Javascript function but the output I'm getting is not freshly populating the 2nd dropdown. On change of a selection, the new list is just getting appended to the old list.

function changecat() {
    var selectHTML = "";

    var A = ["Soup", "Juice", "Tea", "Others"];
    var B = ["Soup", "Juice", "Water", "Others"];
    var C = ["Soup", "Juice", "Coffee", "Tea", "Others"];

    if (document.getElementById("meal").value == "A") {
        var select = document.getElementById('category').options.length;

        for (var i = 0; i < select; i++) {
            document.getElementById('category').options.remove(i);
        }

        for (var i = 0; i < A.length; i++) {
            var newSelect = document.createElement('option');
            selectHTML = "<option value='" + A[i] + "'>" + A[i] + "</option>";
            newSelect.innerHTML = selectHTML;
            document.getElementById('category').add(newSelect);
        }
    }

    else if (document.getElementById("meal").value == "B") {
        var select = document.getElementById('category').options.length;

        for (var i = 0; i < select; i++) {
            document.getElementById('category').options.remove(i);
        }

        for (var i = 0; i < B.length; i++) {
            var newSelect = document.createElement('option');
            selectHTML = "<option value='" + B[i] + "'>" + B[i] + "</option>";
            newSelect.innerHTML = selectHTML;
            document.getElementById('category').add(newSelect);
        }
    }

    else if (document.getElementById("project").value == "C") {
        var select = document.getElementById('category').options.length;

        for (var i = 0; i < select; i++) {
            document.getElementById('category').options.remove(i);
        }

        for (var i = 0; i < C.length; i++) { 
            var newSelect = document.createElement('option');
            selectHTML = "<option value='" + C[i] + "'>" + C[i] + "</option>";
            newSelect.innerHTML = selectHTML;
            document.getElementById('category').add(newSelect);
        }
    }
}

---

HTML-  
<select name="meal" id="meal" onchange="changecat();">
    <option value="">Select</option>
    <option value="A">A</option>
    <option value="B">B</option>
    <option value="C">C</option>
</select>

<select name="category" id="category">
    <option value="">Select</option>
</select>

Answer 1

It might help you

JSFiddle : DEMO

HTML

<select name="meal" id="meal" onChange="changecat(this.value);">
    <option value="" disabled selected>Select</option>
    <option value="A">A</option>
    <option value="B">B</option>
    <option value="C">C</option>
</select>
<select name="category" id="category">
    <option value="" disabled selected>Select</option>
</select>

JS

var mealsByCategory = {
    A: ["Soup", "Juice", "Tea", "Others"],
    B: ["Soup", "Juice", "Water", "Others"],
    C: ["Soup", "Juice", "Coffee", "Tea", "Others"]
}

    function changecat(value) {
        if (value.length == 0) document.getElementById("category").innerHTML = "<option></option>";
        else {
            var catOptions = "";
            for (categoryId in mealsByCategory[value]) {
                catOptions += "<option>" + mealsByCategory[value][categoryId] + "</option>";
            }
            document.getElementById("category").innerHTML = catOptions;
        }
    }

Actually there is kind of loop supported by JavaScript i.e. for...in loop.

A for...in loop only iterates over enumerable properties. Objects created from built–in constructors like Array and Object have inherited non–enumerable properties from Object.prototype and String.prototype, such as String's indexOf() method or Object's toString() method. The loop will iterate over all enumerable properties of the object itself and those the object inherits from its constructor's prototype (properties closer to the object in the prototype chain override prototypes' properties).

In each iteration one property from object is assigned to variable-name and this loop continues till all the properties of the object are exhausted.

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