英文:
How do I use React setState() to set the state to a specific value that is a constant?
问题
const [number, setNumber] = useState(0);
let newNumber = 200;
useEffect(() => {
setNumber(number + 1);
}, [])
我相信我对React.js中状态如何工作有一些误解。如果我将上述代码中的setNumber(number + 1)部分更改为+ 1，如下所示，那么number会变成201，但如果我将其更改为= newNumber，我会收到TypeError: Assignment to constant variable错误。为什么会这样？而且，既然newNumber没有使用const标记，错误不应该是其他什么吗？
英文:
const [number, setNumber] = useState(0);
let newNumber = 200;
useEffect(() => {
setNumber(number = newNumber);
}, [])
I believe I'm misunderstanding something about how state works in React.js. If I set the above code's setNumber(number + 1) section to '+ 1' like so then number becomes '201' but if I set it to '= newNumber' I get a 'TypeError: Assignment to constant variable' error. Why is this the case? And shouldn't the error be something else since newNumber isn't a constant variable using the 'const' tag?
答案1
得分: 2
setNumber函数接受一个你想要设置为状态的值。所以，如果你想将数字设置为新数字的值，你可以这样做：setNumber(newNumber)。
英文:
The setNumber function accepts a value you want to set your state to. So If you want to set number to the value of newNumber you would do setNumber(newNumber)
答案2
得分: 0
只需像这样使用setNumber：
useEffect(() => {
setNumber(newNumber);
}, [])
或者更好地在初始表达式中使用：
const [number, setNumber] = useState(200)
英文:
Just use setNumber like
useEffect(() => {
setNumber(newNumber);
}, [])
or better just in initial expression
const [number, setNumber] = useState(200)
答案3
得分: 0
只需将您的值放入 setNumber 函数中。
const [number, setNumber] = useState(0);
let newNumber = 200;
useEffect(() => {
setNumber(newNumber);
}, [])
英文:
Just put your values inside setNumber function.
const [number, setNumber] = useState(0);
let newNumber = 200;
useEffect(() => {
setNumber(newNumber);
}, [])
答案4
得分: 0
useState描述了状态，它可以是一个对象、字符串、布尔值和数字。如果它是一个原始数据，而不是一个对象，你只需要在更新时传递值，如下所示：
setStateVal(5); // 这里的5将成为新的状态
如果你的状态是一个对象，你需要按照以下方式传递更新后的状态对象：
setStateVal({ val: 5 });
无论如何，都不要使用=运算符。
英文:
useState describe the state, it can be an object, string, boolean and a number. In case its a primitive data i.e not an object, you just need to pass the value while updating it as follows:
setStateVal(5); // here 5 will become the new state
In case your state is an object, you need to pass the updated state object as follows:
setStateVal({val: 5});
In no case you use = operator.
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