了解es6函数的工作原理

Question

我已经在代码库中编写了这段代码，但是我无法理解它的工作原理。

   // this method of writing ((value) after arrow 
   dataOnChange = (index) => ((value) => {
    let dataoptions = this.state.options.map((item, itemIndex) => {
        if(itemIndex === index) {
            return value;
        }
        return item;
    });
    // setting the state here with dataoptions which is not at all a concren      
});