How to make marquee text only when it's overflowing?

Question

I have a text which is generated randomly to a div. And this text has different width depending on what is currently generated. And I want this text to marquee only when is too big. html:

<div id="random_word"> <!--here appears something--> </div>

css:

#random_word {
    color: white;
    position: absolute;
    width: 50%;
    left: 0%;
    text-align: center;
    font-size: 8vw;
    margin-top: 22%;
    font-variant: small-caps
    text-shadow: 0 0 20px #000;
    text-align: center;
    z-index: 2;
    overflow: hidden;
    white-space: nowrap;
    line-height: 100%;
}

I found already this css property in internet: overflow-x:-webkit-marquee; but I'm not sure how to use it. Can anyone help?

Answer 1

The easiest way to determine if an element is overflowing is to compare its scroll height/width to its offset height/width. If any of the scroll values are larger than their offset pairs, your element's contents are overflowing.

function isElementOverflowing(element) {
    var overflowX = element.offsetWidth < element.scrollWidth,
        overflowY = element.offsetHeight < element.scrollHeight;

    return (overflowX || overflowY);
}

From here it's a simple question of checking the return value of this function and adding a marquee effect if true. To achieve this, you can wrap your div's contents in a <marquee>, or achieve the same visual effect using the prefixed marquee CSS rules or simulating it via a CSS animation.

NB: while the <marquee> tag still works as expected in most browsers, it is considered deprecated hence not futureproof.

• Here is a quick fiddle on wrapping in a marquee tag, play around with text length to see how it works. (alternatively, you can set the marquee's behavior to alternate from side to side: here's how )
• here is a tutorial on CSS marquee
• and here is a thread on visually simulating a marquee with animations

Good luck!