// Save search term state to React Hooks with spread operator and wrapper function

// Using .concat(), no wrapper function (not recommended)
setSearches(searches.concat(query))

// Using .concat(), wrapper function (recommended)
setSearches(searches => searches.concat(query))

// Spread operator, no wrapper function (not recommended)
setSearches([...searches, query])

// Spread operator, wrapper function (recommended)
setSearches(searches => [...searches, query])

https://medium.com/javascript-in-plain-english/how-to-add-to-an-array-in-react-state-3d08ddb2e1dc

如果你想推特定的索引，你可以这样做:

   const handleAddAfterIndex = index => {
       setTheArray(oldItems => {
            const copyItems = [...oldItems];
            const finalItems = [];
            for (let i = 0; i < copyItems.length; i += 1) {
                if (i === index) {
                    finalItems.push(copyItems[i]);
                    finalItems.push(newItem);
                } else {
                    finalItems.push(copyItems[i]);
                }
            }
            return finalItems;
        });
    };

setTheArray([…theArray newElement]);是最简单的答案，但要注意数组中项目的突变。使用数组项的深度克隆。

最推荐的方法是同时使用包装函数和展开运算符。例如，如果你像这样初始化了一个名为name的状态，

控制[names, setNames] = useState(]

你可以像这样推到这个数组，

setNames(names => [...names, newName])

希望这能有所帮助。

为了进一步展开， 这里有一些常见的例子。开始:

const [theArray, setTheArray] = useState(initialArray);
const [theObject, setTheObject] = useState(initialObject);

在数组的末尾推入元素

setTheArray(prevArray => [...prevArray, newValue])

在对象的末尾推/更新元素

setTheObject(prevState => ({ ...prevState, currentOrNewKey: newValue}));

在对象数组的末尾推/更新元素

setTheArray(prevState => [...prevState, {currentOrNewKey: newValue}]);

将元素推到数组对象的末尾

let specificArrayInObject = theObject.array.slice();
specificArrayInObject.push(newValue);
const newObj = { ...theObject, [event.target.name]: specificArrayInObject };
theObject(newObj);

这里也有一些实际的例子。 https://codesandbox.io/s/reacthooks-push-r991u

// Save search term state to React Hooks with spread operator and wrapper function

// Using .concat(), no wrapper function (not recommended)
setSearches(searches.concat(query))

// Using .concat(), wrapper function (recommended)
setSearches(searches => searches.concat(query))

// Spread operator, no wrapper function (not recommended)
setSearches([...searches, query])

// Spread operator, wrapper function (recommended)
setSearches(searches => [...searches, query])

https://medium.com/javascript-in-plain-english/how-to-add-to-an-array-in-react-state-3d08ddb2e1dc