display table-cell fill available

fiddle to help out look997 on ask.m.o

HTML

<div id="plus-relation" > <div class="xplus-icon" style="width: 20px; height: 20px; background: red;"></div> </div>

JavaScript

function xwidgetClass() {
    
    this.someVar = 123;
    
    var self = this;    
    
document.querySelector("#plus-relation").addEventListener("click", function (){
    self.plusRelation(arguments[0], this).bind(self)
}, false);
}
xwidgetClass.prototype.plusRelation = function (event, _this) {

    console.log(event.target);
    console.log(_this);
    console.log(this);
}
new xwidgetClass();