经常在项目中遇到这样的写法：
[SOME_MUTATION] (state) {
// mutate state
}在es6中字面量定义对象时，用表达式作为对象的属性名，把表达式放在方括号内
const SOME_MUTATION = 'SOME_MUTATION'
var mutations = {}
mutations[SOME_MUTATION] = function (state) {
// mutate state
}
//相当于对象的属性打点调用和中括号调用原文：https://www.cnblogs.com/my466879168/p/12236819.html