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


my requirement selection in 'meal' drop down list, second drop down list 'category' should dynamically populated values related selection in first drop down list. depending on selected in meal dropdown, list should change in category. have written following javascript function output i'm getting not freshly populating 2nd dropdown. on change of selection, new list getting appended old list. 

function changecat() {     var selecthtml = "";      var = ["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;          (var = 0; < select; i++) {             document.getelementbyid('category').options.remove(i);         }          (var = 0; < 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;          (var = 0; < select; i++) {             document.getelementbyid('category').options.remove(i);         }          (var = 0; < 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;          (var = 0; < select; i++) {             document.getelementbyid('category').options.remove(i);         }          (var = 0; < 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>

it might 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 = "";             (categoryid in mealsbycategory[value]) {                 catoptions += "<option>" + mealsbycategory[value][categoryid] + "</option>";             }             document.getelementbyid("category").innerhtml = catoptions;         }     }

actually there kind of loop supported javascript i.e. for...in loop.

a for...in loop iterates on enumerable properties. objects created built–in constructors array , object have inherited non–enumerable properties object.prototype , string.prototype, such string's indexof() method or object's tostring() method. loop iterate on enumerable properties of object , object inherits constructor's prototype (properties closer object in prototype chain override prototypes' properties).

in each iteration 1 property object assigned variable-name , loop continues till properties of object exhausted.

for more link


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