Elements in iteration expect to have 'v-bind:key' directives

[zsyoung]

<span v-if="spaceIconShow(index)" v-for="(space, levelIndex) in scope.row._level" class="ms-tree-space"></span>

这句话编译时候会报错， 在在v-for后面加上:key='(space, levelIndex)'，问题解决