typescript使用可选属性报错可能未定义

当使用可选属性时，会报错 参数可能未定义

例如:

interface actionType {
    
    
  type: string
  increaseNum?: number
  decreaseNum?: number
}
export const operateNum = (state = defaultState, action: actionType) => {
    
    
  switch (action.type) {
    
    
    case operation.ADD:
      return {
    
     ...state, ...{
    
     num: state.num + action.increaseNum } }
    case operation.DEL:
      return {
    
     ...state, ...{
    
     num: state.num - action.decreaseNum } }
  }
}

解决方法是在tsconfig.json中修改strict属性为false，取消严格模式就好了

"compilerOptions": {
    
    
	"strict":false
	}