JSFiddle - React, Tailwind, and code Playground

HTML

<div id="projectList"></div>

CSS

.row-fluid {
    border-color: black;
    background: red;
}

JavaScript

var i = 0;
var json = {
    projects: [{
        title: "t1",
        description: "d1"
    }, {
        title: "t2",
        description: "d2"
    }, {
        title: "t3",
        description: "d3 "
    }, {
        title: "t4 ",
        description: "d4 "
    }, {
        title: "t5 ",
        description: " d5 "
    }]
};

function myjson(json) {
    $.each(json.projects, function (index, data) {
        //some stuff to find and filter my data
        $('<div/>', {
            "id": index,
          "class": "span4",
           html: '<h3>' + data.title + '</h3>' + data.description
        }).appendTo('#projectList');
        
    });
}

function test() {
    myjson(json);
    var divs = $('#projectList > div');
    for (var i = 0; i < divs.length; i += 3) {
        divs.slice(i, i + 3).wrapAll('<div class="row-fluid "></div>');
    }
}
test();