compare plus operator vs plus equal operator

var html = '';
html =   '<div class="c-item">' +
            '<a href="#" class="c-img">' +
                '<img class="border-img" src="http://www.newyorker.com/online/blogs/photobooth/NASAEarth-01.jpg?_=1384308019032" width="100px" height="100px">' +
            '</a>' +
            '<div class="c-info">' +
                '<p class="c-name">C-NAME</p>' +
                '<p class="desc">I once worked with a development team that eschewed the use of JavaScript because it was difficult to test. Now this was a few years back, but maybe they didn\'t look very hard for JS testing frameworks. </p>' +
                '<p class="c-code">' +
                    '<strong>Code</strong>' +
                    '<a class="btn-code">ABCDEFGH</a>' +
                    '<span class="g-until">' +
                        '<strong>Good Until:</strong>' +
                        '<span class="date">13/11/2013</span>' +
                    '</span>' +
                    '<label class="overlay">' +
                        '<input type="text" value="ABCDEFGH"/>' +
                        'Copy code then click' +
                        '<a class="btn" href="#">Click here</a>' +
                    '</label>' +
                '</p>' +
                '<a class="c-link" href="#">See all c-links &raquo;</a>' +
            '</div>' +
        '</div>';

var html = '';
html += '<div class="c-item">';
html += '<a href="#" class="c-img">';
html += '<img class="border-img" src="http://www.newyorker.com/online/blogs/photobooth/NASAEarth-01.jpg?_=1384308019032" width="100px" height="100px">';
html += '</a>';
html += '<div class="c-info">';
html += '<p class="c-name">C-NAME</p>';
html += '<p class="desc">I once worked with a development team that eschewed the use of JavaScript because it was difficult to test. Now this was a few years back, but maybe they didn\'t look very hard for JS testing frameworks. </p>';
html += '<p class="c-code">';
html += '<strong>Code</strong>';
html += '<a class="btn-code">ABCDEFGH</a>';
html += '<span class="g-until">';
html += '<strong>Good Until:</strong>';
html += '<span class="date">13/11/2013</span>';
html += '</span>';
html += '<label class="overlay">';
html += '<input type="text" value="ABCDEFGH"/>';
html += 'Copy code then click';
html += '<a class="btn" href="#">Click here</a>';
html += '</label>';
html += '</p>';
html += '<a class="c-link" href="#">See all c-links &raquo;</a>';
html += '</div>';
html += '</div>';