the layout of the page does not change with js

Basically I have written a basic code but cannot figure out where is the issue causing it not to work.

so I have the following DOM snippet

<div class="container" id="page-layout">
    <h1>Lets start <span>getting a little</span> more fancy!</h1>
    <img src="../images/tiger.jpg" alt="tiger image">

    <div class="columns" >
        <div class="col col-1">
            <h2>Dolor sit</h2>
            <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Fugiat distinctio quo ratione vitae cupiditate aliquid eos magni quisquam nesciunt commodi perferendis, et maiores molestias similique quam illo dolorum consequatur. Repellat!</p> <!--30-->
        </div> 
</div>

and my script is working as following

 var pageLayout = document.getElementById("page-layout");
    document.getElementById("contact-page").onclick = function () { pageLayout[0].innerHTML = "<p>this is the contact page</p>";
}

I have taken container by is and not the body because i have the header and the footer in the page that i would like to have remaining in there and only change the inner container layout. What could cause the problem here? I have tried to change the information in the header of my page selecting the element by class and the second line of the js seemed to work perfectly, so the issue lies with my selection of the container by the id?

snippet of the header

   <header>
        <div class="container container-nav">
        <div class="title">
        <h1 id="title-header"> My header  </h1>
        <p class="sub-title">A blog about something </p>


        </div>
        <nav>
            <ul>
                <li><a href="#" class="current-page">Home</a></li>
                <li><a href="#">About</a></li>
                <li><a href="#" id="contact-page">Contact</a></li>
            </ul>
        </nav>
        </div> <!--close of the container-->
    </header>

Answer

One thing I found was wrong while looking through your code is in these lines of code:

var pageLayout = document.getElementById("page-layout");

document.getElementById("contact-page").onclick = function () { 
    pageLayout[0].innerHTML = "<p>this is the contact page</p>";
}

Where you wrote pageLayout[0]. Since the getElementById() function does not return an array, you should get rid of the “[0]” and just write this in the script:

var pageLayout = document.getElementById("page-layout");

document.getElementById("contact-page").onclick = function () { 
    pageLayout.innerHTML = "<p>this is the contact page</p>";
}