阅读更多按钮或显示/隐藏的PHP

I want to show only e.g. 200 words from post with show/hide button to show whole post and hide post to 200 words. Text is on variable I don't know how to do this. I tried with javascript but I can't hide content of post.

here's the:

<div id="test">content</div>
<script>
    var str = "<?=$row[3]?>"; 
    var test = str.substr(0, 700);
    document.getElementById('test').innerHTML = test;
</script>
<p id="demo"></p>
<script>
    function myFunction() {
        var str = "<?=$row[3]?>"; 
        var test = str.substr(700);
        document.getElementById("demo").innerHTML = test;
    }
</script>
<button onclick="myFunction()">Click me</button>

You can do that in simple css

Don't need any other

hide your overflow text

modify code in css according to your need

/* css only show/hide

 */

html { background: white }

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

figure {
    margin: 0 0 1.3rem 0;
    -webkit-transition: .125s linear;
    -moz-transition: .125s linear;
    -ms-transition: .125s linear;
    -o-transition: .125s linear;
    transition: .125s linear;
}

figure img {
    max-width: 100%;
    height: auto;
}

body {
    max-width: 480px;
    width: 90%;
    margin: 3em auto;
    font-size: 75%;
    line-height: 1.3rem;
    font-family: sans-serif;
    position: relative;
    *zoom: 1;
}

body:before, body:after {
    content: "";
    display: table;
}

body:after { clear: both }

p { margin-bottom: 1.3rem }

article {
    margin-bottom: 3rem;
    position: relative;
    *zoom: 1;
}

article:before, article:after {
    content: "";
    display: table;
}

article:after { clear: both }

article figure {
    float: left;
    width: 32.5%;
}

article section:first-of-type {
    float: right;
    width: 62.5%;
}

article section:last-of-type {
    display: none;
    visibility: hidden;
}

section {
    -webkit-transition: .125s linear;
    -moz-transition: .125s linear;
    -ms-transition: .125s linear;
    -o-transition: .125s linear;
    transition: .125s linear;
}

input[type=checkbox] {
    border: 0;
    clip: rect(0 0 0 0);
    height: 1px;
    width: 1px;
    margin: -1px;
    overflow: hidden;
    padding: 0;
    position: absolute;
}

[for="read_more"] {
    position: absolute;
    bottom: -3rem;
    left: 0;
    width: 100%;
    text-align: center;
    padding: .65rem;
    box-shadow: inset 1px 1px rgba(0, 0, 0, 0.1), inset -1px -1px rgba(0, 0, 0, 0.1);
}

[for="read_more"]:hover {
    background: rgba(0,0,0,.5);
    color: rgb(255,255,255);
}

[for="read_more"] span:last-of-type {
    display: none;
    visibility: hidden;
}

input[type=checkbox]:checked ~ section {
    display: block;
    visibility: visible;
    width: 100%;
}

input[type=checkbox]:checked ~ figure { width: 100% }

input[type=checkbox]:checked ~ [for="read_more"] span:first-of-type {
    display: none;
    visibility: hidden;
}

input[type=checkbox]:checked ~ [for="read_more"] span:last-of-type {
    display: block;
    visibility: visible;
}

<article>
    

    <input type="checkbox" id="read_more" role="button">
    <label for="read_more" onclick=""><span>Read More</span><span>Hide This Shit!</span></label>     
      
    <figure>
        <img src="http://www.surprisegiftz.com/images/media/ceramicphototiles.jpg" alt="Example text" />
    </figure>

    <section>
    <p>The function of a paragraph is to mark a pause, setting the paragraph apart from what precedes it. If a paragraph is preceded by a title or subhead, the indent is superfluous and can therefore be omitted</p>
    </section>    



<section>
    <p>The function of a paragraph is to mark a pause, setting the paragraph apart from what precedes it. If a paragraph is preceded by a title or subhead, the indent is superfluous and can therefore be omitted</p>
    <p>The function of a paragraph is to mark a pause, setting the paragraph apart from what precedes it. If a paragraph is preceded by a title or subhead, the indent is superfluous and can therefore be omitted</p>

</section>

</article>

</div>

You dont need to add two seperate elements for short and full content. Just make a hyperlink which will call a script to show hide full and short content.

use below html

<div id="test">content</div>
<div >
    <a href="#" id="showmore" onClick="return showMore(this);" >more</a>

</div>

and below script for it

var str = "<?=$row[3]?>"; 
var test = str.substr(0, 200);
document.getElementById('test').innerHTML = test;

function showMore(obj){
    if(obj.text == 'more'){
document.getElementById('test').innerHTML = str;
        obj.text = "less";
    }else{
    document.getElementById('test').innerHTML = test;
         obj.text = "more";
    }
}

hope it will help