Tab content loaded by default

Question

This might be a trivial question but I would like to know how to have a particular tab opened as the page loads itself. In the following, only the tab menus are there and the contents are loaded after clicking on either one of the tabs. Instead of that, can I have, for example, the tab menu and the contents of "London" loaded and visible as the page loads?

function openCity(evt, cityName) {
    // Declare all variables
    var i, tabcontent, tablinks;

    // Get all elements with class="tabcontent" and hide them
    tabcontent = document.getElementsByClassName("tabcontent");
    for (i = 0; i < tabcontent.length; i++) {
        tabcontent[i].style.display = "none";
    }

    // Get all elements with class="tablinks" and remove the class "active"
    tablinks = document.getElementsByClassName("tablinks");
    for (i = 0; i < tablinks.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" active", "");
    }

    // Show the current tab, and add an "active" class to the link that opened the tab
    document.getElementById(cityName).style.display = "block";
    evt.currentTarget.className += " active";
}

 /* Style the list */
ul.tab {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
}

/* Float the list items side by side */
ul.tab li {float: left;}

/* Style the links inside the list items */
ul.tab li a {
    display: inline-block;
    color: black;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    transition: 0.3s;
    font-size: 17px;
}

/* Change background color of links on hover */
ul.tab li a:hover {background-color: #ddd;}

/* Create an active/current tablink class */
ul.tab li a:focus, .active {background-color: #ccc;}

/* Style the tab content */
.tabcontent {
    display: none;
    padding: 6px 12px;
    border: 1px solid #ccc;
    border-top: none;
}

 <ul class="tab">
  <li><a href="#" class="tablinks" onclick="openCity(event, 'London')">London</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Paris')">Paris</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Tokyo')">Tokyo</a></li>
</ul>

<div id="London" class="tabcontent">
  <h3>London</h3>
  <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="tabcontent">
  <h3>Paris</h3>
  <p>Paris is the capital of France.</p>
</div>

<div id="Tokyo" class="tabcontent">
  <h3>Tokyo</h3>
  <p>Tokyo is the capital of Japan.</p>
</div>

Answer 1

Your can do this in css define your tabcontent first display block as like this

.tabcontent:nth-of-type(1){display:block;}

function openCity(evt, cityName) {
    // Declare all variables
    var i, tabcontent, tablinks;

    // Get all elements with class="tabcontent" and hide them
    tabcontent = document.getElementsByClassName("tabcontent");
    for (i = 0; i < tabcontent.length; i++) {
        tabcontent[i].style.display = "none";
    }

    // Get all elements with class="tablinks" and remove the class "active"
    tablinks = document.getElementsByClassName("tablinks");
    for (i = 0; i < tablinks.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" active", "");
    }

    // Show the current tab, and add an "active" class to the link that opened the tab
    document.getElementById(cityName).style.display = "block";
    evt.currentTarget.className += " active";
}

 /* Style the list */
ul.tab {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
}

/* Float the list items side by side */
ul.tab li {float: left;}

/* Style the links inside the list items */
ul.tab li a {
    display: inline-block;
    color: black;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    transition: 0.3s;
    font-size: 17px;
}

/* Change background color of links on hover */
ul.tab li a:hover {background-color: #ddd;}

/* Create an active/current tablink class */
ul.tab li a:focus, .active {background-color: #ccc;}

/* Style the tab content */
.tabcontent {
    display: none;
    padding: 6px 12px;
    border: 1px solid #ccc;
    border-top: none;
}
.tabcontent:nth-of-type(1){display:block;}

 <ul class="tab">
  <li><a href="#" class="tablinks" onclick="openCity(event, 'London')">London</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Paris')">Paris</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Tokyo')">Tokyo</a></li>
</ul>

<div id="London" class="tabcontent">
  <h3>London</h3>
  <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="tabcontent">
  <h3>Paris</h3>
  <p>Paris is the capital of France.</p>
</div>

<div id="Tokyo" class="tabcontent">
  <h3>Tokyo</h3>
  <p>Tokyo is the capital of Japan.</p>
</div>

============ 2nd option is you can deinfe in html by default show to one

function openCity(evt, cityName) {
    // Declare all variables
    var i, tabcontent, tablinks;

    // Get all elements with class="tabcontent" and hide them
    tabcontent = document.getElementsByClassName("tabcontent");
    for (i = 0; i < tabcontent.length; i++) {
        tabcontent[i].style.display = "none";
    }

    // Get all elements with class="tablinks" and remove the class "active"
    tablinks = document.getElementsByClassName("tablinks");
    for (i = 0; i < tablinks.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" active", "");
    }

    // Show the current tab, and add an "active" class to the link that opened the tab
    document.getElementById(cityName).style.display = "block";
    evt.currentTarget.className += " active";
}

 /* Style the list */
ul.tab {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
}

/* Float the list items side by side */
ul.tab li {float: left;}

/* Style the links inside the list items */
ul.tab li a {
    display: inline-block;
    color: black;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    transition: 0.3s;
    font-size: 17px;
}

/* Change background color of links on hover */
ul.tab li a:hover {background-color: #ddd;}

/* Create an active/current tablink class */
ul.tab li a:focus, .active {background-color: #ccc;}

/* Style the tab content */
.tabcontent {
    display: none;
    padding: 6px 12px;
    border: 1px solid #ccc;
    border-top: none;
}

 <ul class="tab">
  <li><a href="#" class="tablinks active" onclick="openCity(event, 'London')">London</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Paris')">Paris</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Tokyo')">Tokyo</a></li>
</ul>

<div id="London" class="tabcontent" style=display:block;>
  <h3>London</h3>
  <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="tabcontent">
  <h3>Paris</h3>
  <p>Paris is the capital of France.</p>
</div>

<div id="Tokyo" class="tabcontent">
  <h3>Tokyo</h3>
  <p>Tokyo is the capital of Japan.</p>
</div>

Answer 2

try

.tabcontent:first-child{
    display:block;
}

Answer 3

One solution can be to simulate a click.

add this :

document.getElementsByClassName("tablinks")[0].click();

function openCity(evt, cityName) {
    // Declare all variables
    var i, tabcontent, tablinks;

    // Get all elements with class="tabcontent" and hide them
    tabcontent = document.getElementsByClassName("tabcontent");
    for (i = 0; i < tabcontent.length; i++) {
        tabcontent[i].style.display = "none";
    }

    // Get all elements with class="tablinks" and remove the class "active"
    tablinks = document.getElementsByClassName("tablinks");
    for (i = 0; i < tablinks.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" active", "");
    }

    // Show the current tab, and add an "active" class to the link that opened the tab
    document.getElementById(cityName).style.display = "block";
    evt.currentTarget.className += " active";
}

document.getElementsByClassName("tablinks")[0].click();

/* Style the list */
ul.tab {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
}

/* Float the list items side by side */
ul.tab li {float: left;}

/* Style the links inside the list items */
ul.tab li a {
    display: inline-block;
    color: black;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    transition: 0.3s;
    font-size: 17px;
}

/* Change background color of links on hover */
ul.tab li a:hover {background-color: #ddd;}

/* Create an active/current tablink class */
ul.tab li a:focus, .active {background-color: #ccc;}

/* Style the tab content */
.tabcontent {
    display: none;
    padding: 6px 12px;
    border: 1px solid #ccc;
    border-top: none;
}

<ul class="tab">
  <li><a href="#" class="tablinks" onclick="openCity(event, 'London')">London</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Paris')">Paris</a></li>
  <li><a href="#" class="tablinks" onclick="openCity(event, 'Tokyo')">Tokyo</a></li>
</ul>

<div id="London" class="tabcontent">
  <h3>London</h3>
  <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="tabcontent">
  <h3>Paris</h3>
  <p>Paris is the capital of France.</p>
</div>

<div id="Tokyo" class="tabcontent">
  <h3>Tokyo</h3>
  <p>Tokyo is the capital of Japan.</p>
</div>