CODEWITHSUNDEEP
javascriptvisual-studiocordova
Muhammad Haroon Iqbal
Muhammad Haroon Iqbal

Reputation: 552

Uncaught TypeError: Cannot read property 'querySelector' of null

I am using Cordova app in Visual Studio 2015. I have added a simple button which changes the color of background of app to red. but it is giving above mentioned error.

index.html

<!DOCTYPE html>
<html>
    <head>
    <!--
        Customize the content security policy in the meta tag below as needed. Add 'unsafe-inline' to default-src to enable inline JavaScript.
        For details, see http://go.microsoft.com/fwlink/?LinkID=617521
    -->
        <meta http-equiv="Content-Security-Policy" content="default-src 'self' data: gap: https://ssl.gstatic.com 'unsafe-eval'; style-src 'self' 'unsafe-inline'; media-src *">
        
        <meta name="format-detection" content="telephone=no">
        <meta name="msapplication-tap-highlight" content="no">
        <meta name="viewport" content="user-scalable=no, initial-scale=1, maximum-scale=1, minimum-scale=1, width=device-width">
        <link rel="stylesheet" type="text/css" href="css/index.css">
        <title>WeatherApp</title>
    </head>
    <body>
        <p>Hello World</p>
        <input type="button" name="color" value="Change Color" id="color" onclick="changeColor()">
        <script type="text/javascript" src="cordova.js"></script>
        <script type="text/javascript" src="scripts/platformOverrides.js"></script>
        <script type="text/javascript" src="scripts/index.js"></script>
    </body>
</html>

index.js

    (function () {
    "use strict";

    document.addEventListener( 'deviceready', onDeviceReady.bind( this ), false );

    function onDeviceReady() {
        // Handle the Cordova pause and resume events
        document.addEventListener( 'pause', onPause.bind( this ), false );
        document.addEventListener('resume', onResume.bind(this), false);
        
        // TODO: Cordova has been loaded. Perform any initialization that requires Cordova here.
        var parentElement = document.getElementById('deviceready');
        var listeningElement = parentElement.querySelector('.listening');
        var receivedElement = parentElement.querySelector('.received');
        listeningElement.setAttribute('style', 'display:none;');
        receivedElement.setAttribute('style', 'display:block;');

    };


    function onPause() {
        // TODO: This application has been suspended. Save application state here.
    };

    function onResume() {
        // TODO: This application has been reactivated. Restore application state here.
    };

    function changeColor() {
        var change = document.querySelector('#color');
        change.addEventListener('click', change, false);
    }

    function change() {
        var clr = document.querySelector('body');
        clr.style.backgroundColor = 'red';
    }


} )();

enter image description here

Upvotes: 7

Views: 63248

Answers (2)

Hajji Tarik
Hajji Tarik

Reputation: 1082

I think the dom has not yet been loaded, and you try to make a selection so it returns you a null. try to move thoses lines outside the onDeviceReady()

var listeningElement = parentElement.querySelector('.listening');
var receivedElement = parentElement.querySelector('.received');
listeningElement.setAttribute('style', 'display:none;');
receivedElement.setAttribute('style', 'display:block;');

Upvotes: 1

Sir McPotato
Sir McPotato

Reputation: 959

var parentElement = document.getElementById('deviceready');
var listeningElement = parentElement.querySelector('.listening');

You don't have a div with ID deviceready, so your parentElement will be null.

EDIT : I think you can remove this whole block since it's belong to the default cordova page layout when you create a new project :

// TODO: Cordova has been loaded. Perform any initialization that requires Cordova here.
var parentElement = document.getElementById('deviceready');
var listeningElement = parentElement.querySelector('.listening');
var receivedElement = parentElement.querySelector('.received');
listeningElement.setAttribute('style', 'display:none;');
receivedElement.setAttribute('style', 'display:block;');

Upvotes: 5

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