Copy on click

HTML

<p id="content-holder">This text will be inserted into the clipboard.</p>

<button id="copy-button">Copy Text</button>

<textarea id="textareaJs" placeholder="Paste here"></textarea>

CSS

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    padding: 20px;
    font: normal 16px sans-serif;
    color: #555;
}

p {
    margin-bottom: 20px;
}

button {
    padding: 8px 12px;
    margin-bottom: 20px;
}

textarea {
    display: block;
    padding: 10px;
    width: 400px;
    height: 120px;
}

JavaScript

var button = document.getElementById("copy-button");

button.addEventListener("click", function() {
	// we'll take value of button
	var para = document.querySelector("#content-holder").innerHTML;
	// create variable for textarea
	var textarea = document.querySelector("#textareaJs");
	// we'll take value of textarea that is equal to para(text)
	textarea.innerHTML = para;
});