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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

HTML

            
              <svg xmlns="http://www.w3.org/2000/svg" width="0" height="0" viewBox="0 0 100 100">
        <defs>
            <linearGradient id="gradient" x1="0%" y1="0%" x2="100%" y2="0%">
                <stop offset="0%" stop-color="#00bc9b" />
                <stop offset="100%" stop-color="#5eaefd" />
            </linearGradient>
            <linearGradient id="gradient2" x1="0%" y1="0%" x2="100%" y2="0%">
                <stop offset="0%" stop-color="#5eaefd" />
                <stop offset="100%" stop-color="#00bc9b" />
            </linearGradient>
        </defs>
    </svg>
    <div class="group">
        <ul class="c-nav underliner">
            <li class="c-nav__item"><a href="#">News & Politics</a></li>
            <li class="c-nav__item"><a href="#">Culture</a></li>
            <li class="c-nav__item"><a href="#">Technology</a></li>
            <li class="c-nav__item"><a href="#">Business</a></li>
            <li class="c-nav__item"><a href="#">Human Interest</a></li>
        </ul>
        <ul class="c-nav c-nav-2 underliner-small">
            <li class="c-nav__item"><a href="#">Works</a></li>
            <li class="c-nav__item"><a href="#">Articles</a></li>
            <li class="c-nav__item"><a href="#">About</a></li>
            <li class="c-nav__item"><a href="#">Contact Me</a></li>
            <li class="c-nav__item"><a href="#">My Books</a></li>
        </ul>
    </div>


<hr>

<p class="ishadeed">Read the article on <a href="https://ishadeed.com/article/custom-underline-svg/">ishadeed.com</a>. <a href="https://github.com/shadeed/underliner">Github</a></p>
            
          
!

CSS

            
              body {
	padding: 1rem;
	font-family: 'IBM Plex Sans', sans-serif;
}

svg {
	display: block;
}

.group {
	//outline: 1px solid lightgrey;
	padding: 1rem;
	margin-bottom: 2.5rem;
}

.c-nav {
  &:not(:last-child) {
    margin: 1rem 0 2rem;
  }

	@media (min-width: 900px) {
		display: flex;
		justify-content: center;
	}
}

.c-nav__item {
	margin-right: 1.5rem;
	font-size: 1.5rem;

	a {
		display: inline-block;
		text-decoration: none;
		color: #000;
		margin-bottom: 4px;
		transition: 0.4s;
	}

	svg {
		pointer-events: none;
        transition: 0.5s;
        //outline: solid 1px lightgrey;
	}

	path {
        transition: stroke-dasharray 0.5s, stroke-dashoffset 0.5s, opacity 0.5s;
        
        &:last-child {
            opacity: 0.2;
        }
	}

	a {
		&:hover,
		&:focus {
			color: #00bc9b;
		}
	}

	a:hover + svg,
	a:focus + svg {
		opacity: 1;

		path {
			stroke-dashoffset: 0;	
		}
	}
}

#path1 {
	opacity: 0.25;
}

.c-form {
	max-width: 500px;
	margin: 0 auto;

	legend {
		margin-bottom: 1rem;
		font-weight: bold;
	}

	label {
		user-select: none;
	}
}

.c-form__item {
	margin-bottom: 1rem;
}

.c-nav-2 {
	.c-nav__item {
		font-size: 1rem;
	}
}

hr {
  border: 0;
  height: 1px;
  background: lightgrey;
}

.ishadeed {
  text-align: center;
  
  a {
    color: #3563D9;
  }
}
            
          
!

JS

            
              class Underliner {
    constructor(selector, color1, color2, thickness1, thickness2, strokeLinecap, rtl) {
        this.links = document.querySelectorAll(selector)
        this.fill = 'transparent';
        this.color1 = color1;
        this.color2 = color2;
        this.thickness1 = thickness1;
        this.thickness2 = thickness2;
        this.strokeLinecap = strokeLinecap;
        this.rtl = rtl;
        this.init();
    }

    init() {
        let self = this;

        self.links.forEach(function (link) {
            let linkWidth = parseInt(link.offsetWidth);
            let svg = self.createSVG(linkWidth);
            self.insertAfter(svg, link);
        });
    }

    setPath(pathD, color, thickness, strokeLinecap) {
        const path = document.createElementNS("http://www.w3.org/2000/svg", "path");

        path.setAttribute("d", pathD);
        path.setAttribute("fill", this.fill);
        path.setAttribute("stroke", color);
        path.setAttribute("stroke-width", thickness);
        path.setAttribute("stroke-linecap", strokeLinecap);
        path.setAttribute("stroke-dasharray", path.getTotalLength() + 10);
        path.setAttribute("stroke-dashoffset", path.getTotalLength() + 10);

        return path;
    }

    randomizePath(linkWidth) {
        let moveYMin = 5;
        let moveYMax = 12;

        let curveXMin = 15;
        let curveXMax = linkWidth; /* Width of the link */
        let curveYMin = 7;
        let curveYMax = linkWidth * 0.12; /* Making the quadratic propotional to the link width */
        //let curveYMax = 20

        let endYMin = 5;
        let endYMax = 11;

        let moveY = Math.floor(Math.random() * (moveYMax - moveYMin)) + moveYMin;
        let curveX = Math.floor(Math.random() * (curveXMax - curveXMin)) + curveXMin;
        let curveY = Math.floor(Math.random() * (curveYMax - curveYMin)) + curveYMin;
        let endY = Math.floor(Math.random() * (endYMax - endYMin)) + endYMin;

        return `M5 ${moveY} Q ${curveX} ${curveY} ${linkWidth - 7} ${endY}`
    }

    createSVG(linkWidth) {
        const svg = document.createElementNS("http://www.w3.org/2000/svg", "svg");

        svg.setAttribute("width", linkWidth);
        svg.setAttribute("height", "35");

        const path = document.createElementNS("http://www.w3.org/2000/svg", "path");
        const path2 = document.createElementNS("http://www.w3.org/2000/svg", "path");

        let pathD = this.randomizePath(linkWidth);
        let pathD2 = this.randomizePath(linkWidth);

        if(this.rtl === true) {
            pathD = this.reverseMe(pathD);
            pathD2 = this.reverseMe(pathD2);
        }

        svg.appendChild(this.setPath(pathD, this.color1, this.thickness1, this.strokeLinecap));
        svg.appendChild(this.setPath(pathD2, this.color2, this.thickness2, this.strokeLinecap));

        svg.setAttribute("focusable", false);

        return svg;
    }

    reverseMe(path) {
        /* Regex functions borrwed from 
        https://github.com/krispo/svg-path-utils/blob/master/src/svg-path-utils.js */
        let pathOperators = path.replace(/[\d,\-\s]+/g, '').split('');
        let pathNums = path.replace(/[A-Za-z,]+/g, ' ').trim().replace(/\s\s+/g, ' ').split(' ');
    
        return `${pathOperators[0]} ${pathNums[4]} ${pathNums[5]} ${pathOperators[1]} ${pathNums[2]} ${pathNums[3]} ${pathNums[0]} ${pathNums[1]}`;
    }

    // https://plainjs.com/javascript/manipulation/insert-an-element-after-or-before-another-32/
    insertAfter(el, referenceNode) {
        referenceNode.parentNode.insertBefore(el, referenceNode.nextSibling);
    }
}

let test = new Underliner(".underliner a", "url(#gradient)", "url(#gradient2)", 7, 12, "round", false);

let test2 = new Underliner(".underliner-small a", "url(#gradient)", "url(#gradient2)", 3, 6, "round");
            
          
!
999px

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