Javascript regex:将Emojione img转换为短名称

Question

var test = '<img class="emojione" src="https://cdnjs.cloudflare.com/ajax/libs/emojione/2.1.4/assets/png/1f600.png?v=2.2.5" alt=":grinning:" /><img class="emojione" src="https://cdnjs.cloudflare.com/ajax/libs/emojione/2.1.4/assets/png/1f621.png" alt=":rage:" />';
test = test.replace(/<img.*?class="emojione".*?alt="(.*)?".*?>/g, '$1');
console.log(test);

在javascript regex上帮我一下。我希望输出是":grinning::rage:“。仅当只有一个img时，此正则表达式才有效