Cкрыть часть текста

function more() { 
    var p = $('p'); 
	p.toggleClass('open'); 
    if(p.hasClass('open')) { 
        p.css('max-height', p.prop('scrollHeight')); 
    } else { 
        p.css('max-height', 38); 
    } 
}

p { 
    position: relative; 
    overflow: hidden; 
    max-height: 38px; 
    transition: 0.3s; 
} 
 
p:after { 
    content: ''; 
    position: absolute; 
    bottom: 0; 
    left: 0; 
    right: 0; 
    box-shadow: inset #fff 0 -30px 20px -15px; 
    height: 30px; 
} 
 
p.open:after { 
    height: 0; 
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
<p> 
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloribus voluptate eveniet ut asperiores libero ipsa, corrupti, rerum iste adipisci pariatur ipsum numquam dolore eius aut aliquid, nulla facilis odio dicta. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloribus voluptate eveniet ut asperiores libero ipsa, corrupti, rerum iste adipisci pariatur ipsum numquam dolore eius aut aliquid, nulla facilis odio dicta. 
</p> 
<button onclick="more();">Читать далее</button>

function more() { 
    var p = document.querySelector('p'); 
    p.classList.toggle('open'); 
    if(p.classList.contains('open')) { 
        p.style.maxHeight = p.scrollHeight+'px'; 
    } else { 
        p.style.maxHeight = '38px'; 
    } 
}

p { 
    position: relative; 
    overflow: hidden; 
    max-height: 38px; 
    transition: 0.3s; 
} 
 
p:after { 
    content: ''; 
    position: absolute; 
    bottom: 0; 
    left: 0; 
    right: 0; 
    box-shadow: inset #fff 0 -30px 20px -15px; 
    height: 30px; 
} 
 
p.open:after { 
    height: 0; 
}

<p> 
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloribus voluptate eveniet ut asperiores libero ipsa, corrupti, rerum iste adipisci pariatur ipsum numquam dolore eius aut aliquid, nulla facilis odio dicta. Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloribus voluptate eveniet ut asperiores libero ipsa, corrupti, rerum iste adipisci pariatur ipsum numquam dolore eius aut aliquid, nulla facilis odio dicta. 
</p> 
<button onclick="more();">Читать далее</button>