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changing innerHTML of child element using javascript

I would like to change my icon from expand_more to expand_less in following code
<li class="dropdown-bt" onclick="dropdown('content');">
<a>dropdown-content <i class="material-icons">expand_more</i></a>
</li>
I am going to use same code multiple times so it would be better to using function multiple times. I thought of using ID for every piece of code but it would be to hectic. So I want to write single function do it but I don't know how, so please help.

Just pass an object event as a parameter, say e to your dropdown() and use the textContent property to retrieve the current element content, check it's value and replace the content with another text content like this:
var btn = document.getElementById("dropdownBt");
function dropdown(e) {
var innerText = e.target.children[0];
if(innerText.textContent == "expand_more") {
innerText.textContent = "expand_less";
} else {
innerText.textContent = "expand_more";
}
}
btn.addEventListener('click', dropdown);
<li class="dropdown-bt" id="dropdownBt"><a>dropdown-content <i class="material-icons">expand_more</i></a></li>

creating a link to images

I am trying to create a jquery code which can wrap an img tag with a link:
My code is like this:
http://prntscr.com/iuw6hc
I will paste my HTML here but basically it is a loop of many items showing within each col.
<div class="car-item gray-bg text-center first" style="height: 357px;">
<div class="car-image">
<img class="img-responsive" src="http:///wp-content/uploads/2018/03/20180214_090633-265x190.jpg" alt="" width="265" height="190">
<div class="car-overlay-banner">
<ul>
<li><i class="fa fa-link"></i></li>
I am trying like this:
var wrapped = false;
var original = $(".img-responsive");
$(".img-responsive").click(function(){
if (!wrapped) {
wrapped = true;
var gURL = $('.car-overlay-banner').find('a').attr('href');
$(".img-responsive").wrap("");
}
});
$(".img-responsive").click(function(){
if (wrapped) {
wrapped = false;
$(".img-responsive").parent().replaceWith(original);
}
});
Trying to use a href of car overlay to apply to the image too.

jQuery provides a method named "wrap()", which can be used to insert any HTML structure in set of matched elements. In simple words, if you want put wrapper around your div element then you can use wrap() method. For example, you have a div with ID "Child".
<div id="Child"></div>
And want to wrap this div with any parent then you can use "wrap()" method to insert HTML.
$('#Child').wrap('<div id="Parent"></div>');
<div id="parent">
<div id="child"></div>
</div>
Same way, we will use the wrap() method to insert hyperlink to image tag so that the image becomes clickable. See below.
$(document).ready(function() {
$("#imgLogo").wrap('');
});
In this example, I have used ID as selector but you can use class selector to find all the images with same class and then wrap them with tag. You can also assign target="_blank" in the above tag to open the link in new window.

I think you need code like this?
var wrapped = false;
var original = $(".img-responsive");
$(".img-responsive").click(function(){
if (!wrapped) {
var wrapped = true;
// find link href in .car-image(img-responsive's parent)
var gURL = $(this).parent().find('a').attr('href');
// use $(this) instead of $(".classname") to apply link only clicked image
$(this).wrap("");
}
});
$(".img-responsive").click(function(){
if (wrapped) {
var wrapped = false;
$(this).parent().replaceWith(original);
}
});

Class not working jQuery

So I more than one dynamicly generated elements with the same class name that I am trying to check input for in jQuery. Instead of it letting me click on both, it is just letting me click the first element generated.
Ex: I click on item_1 and it returns the item_1 id, but when I click on item_2 it doesn't return anyting.
HTML
<div id="item_1" class="resp"></div>
<div id="item_2" class="resp"></div>
JS - Jquery
$(".resp").on("click",() =>{
var id = $(".resp").attr("id");
console.log('attempting toggle' + id);
});

Firstly, you have to use normal function instead of arrow function (to avoid missing the context). Secondly - use this keyword to refer to the actually clicked element.
$(".resp").on("click", function() {
console.log('attempting toggle ' + this.id);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="item_1" class="resp">A</div>
<div id="item_2" class="resp">B</div>

This is because .attr('id') returns the value of the id attribute of the first matched element in the set.
Instead, use an old school function for the handler so the this value is equal to the clicked div, then get its id:
$(".resp").on("click", function() {
var id = $(this).attr('id');
console.log('attempting toggle ' + id);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="item_1" class="resp">First</div>
<div id="item_2" class="resp">Second</div>

What you're doing here is referencing the classname to obtain the id. This gathers the id of the first classname, which isn't what you desire. What you need to do is use the this keyword to correctly obtain the id.
After removing the arrow function and changing the internal code a bit, it should look like this:
$(".resp").on("click", function() {
var id = this.id;
console.log('attempting toggle: ' + id);
});
Also make sure you've correctly installed JQuery. Pick up your JQuery embed code from here.
Also remember to include your JQuery code before your JavaScript code.

jQuery select the function selector

I'm trying to achieve something inside a function, to actually access the parent selector.
Here is a small snippet of my HTML code:
<div class="module-row module-tab pull-right" id="modtab-sql_net">
<img src="images/icons/icon-orangebox-plus.png" class="modtab-toggle">
</div>
<div id="tab-module-row-1">
</div>
<div class="module-row module-tab pull-right" id="modtab-sql_dss">
<img src="images/icons/icon-orangebox-plus.png" class="modtab-toggle">
</div>
<div id="tab-module-row-2">
</div>
Here is the jQuery script I tried:
$('div[id^="modtab-"]').click(function(){
$(this).next('div[id^="tab-module-row"]').toggle(function(){
$(this).next('.modtab-toggle').toggle_switch.attr("src").replace("plus", "minus");
// The above line is incorrect. I need to change img attr for the class which is inside the div being clicked
});
});
Now, I want to actually change the image icon from a "plus" to a "minus" (the filenames are kept such).
I need to change $(this).next('.modtab-toggle') in the code to something that can work.
Please do NOT suggest to simply access the class using $('.modtab-toggle') as I have multiple such div tags in the code. It won't work out that way.
Thanks for any help.

Try this:
$('div[id^="modtab-"]').click(function(){
$(this).find('.modtab-toggle').attr("src", function(i, attr){
var o = this.src.indexOf('plus') > -1 ? this.src.replace('plus', 'minus') : this.src.replace('minus', 'plus');
return o;
});
});
See the Demo # Fiddle

try something like this
$('div[id^="modtab-"]').click(function(){
var $this = $(this);// clicked div
$this.next('.tab-module-row').toggle(function(){
$this.find('.modtab-toggle').toggle_switch.attr("src").replace("plus", "minus");
});
});
Note: you should use class instead of id because it should be unique
#tab-module-row ->.tab-module-row
EDITED ANSWER
$('div[id^="modtab-"]').click(function(){
var $this = $(this);// clicked div
$this.next('div[id^="tab-module-row"]').toggle(function(){
var img = $this.find('.modtab-toggle'); // your image object
// your condition to check which image to display will goes here.
});
});

change $(this).next('.modtab-toggle') to $(this).find('.modtab-toggle') to make it work.
See find() docs here

Jquery detecting clicked element id

I'm trying to use the same function to slide up and down a text area. using jquery's slidetoggle.
How can I make javascript detect the clicked element in order to know which box to expand.
Here is what I have
function slidedown(id){
$(id+'text').slideToggle(500);
}
that is my function
in my html I have this
<a id="reroof" href="javascript:slidedown(this)">reroof</a>
the section i want to expand is called rerooftext
however when I check the value of id.id I says undefined.
Any ideas?

try the following code:
html code:
<a id="reroof" href="#" onclick="javascript:slidedown(this)">reroof</a>
JS code:
function slidedown(val){
var id = val.id;
alert(id);
$(id+'text').slideToggle(500);
}
In html you are passing the element(this refers the element not an id)
Working Example:
http://jsfiddle.net/jAkMq/

In your HTML:
<a id="reroof" href="#">reroof</a>
In your javascript:
$("#reroof").click(function (e) {
var id = "#" + this.id + "text";
$(id).slideToggle(500);
e.preventDefault();
});

try this
<a id="reroof" href="javascript:void(0)" onclick="slidedown(this)">reroof</a>
function slidedown(obj){
$(obj.id+'text').slideToggle(500);
}
javascript:slidedown(this). here this will be the element not the id