js 多個箭頭函數的使用

 

多個箭頭函數，例如：

const navigateOnce = (getStateForAction) => (action, state) => {
    const {type, routeName, params} = action;
    return (
        state &&
        (type === NavigationActions.NAVIGATE) &&
        routeName === state.routes[state.routes.length - 1].routeName &&
        JSON.stringify(params) === JSON.stringify(state.routes[state.routes.length - 1].params)
    ) ? null getStateForAction(action, state);
};

 

箭頭函數的含義：

() => ...
//等價於
(function() {
    return ...
}).bind(this)

 

注意： 箭頭函數在不寫{} 的情況下，可以省略return關鍵字，而默認return接下來的東西

由此可見：類似

() => () => ...

等價於：

() => {return () => {return ...}}

等價於

function () {
    retunrn function() {
        return ...
    }
}

 

綜上，上面函數的意思就是：

const navigateOnce = function(getStateForAction) {
    return (action, state) => {
        const {type, routeName, params} = action;
        return (
            state &&
            (type === NavigationActions.NAVIGATE) &&
            routeName === state.routes[state.routes.length - 1].routeName &&
            JSON.stringify(params) === JSON.stringify(state.routes[state.routes.length - 1].params)
        ) ? null getStateForAction(action, state);
    };
}

即：

const navigateOnce = function(getStateForAction) {
    return function(action, state) {
        const {type, routeName, params} = action;
        return (
            state &&
            (type === NavigationActions.NAVIGATE) &&
            routeName === state.routes[state.routes.length - 1].routeName &&
            JSON.stringify(params) === JSON.stringify(state.routes[state.routes.length - 1].params)
        ) ? null getStateForAction(action, state);
    };
}