通过将光标位置保存在处理程序的开头并在呈现新状态后恢复它，光标位置将始终处于正确位置。
但是，由于添加-会改变光标位置，所以需要考虑它对初始位置的影响
import React, { useRef, useState, useLayoutEffect } from "react";
export default function App() {
const [state, setState] = useState({ phone: "" });
const cursorPos = useRef(null);
const inputRef = useRef(null);
const keyIsDelete = useRef(false);
const handleChange = e => {
cursorPos.current = e.target.selectionStart;
let val = e.target.value;
cursorPos.current -= (
val.slice(0, cursorPos.current).match(/-/g) || []
).length;
let r = /(\D+)/g,
first3 = "",
next3 = "",
last4 = "";
val = val.replace(r, "");
let newValue;
if (val.length > 0) {
first3 = val.substr(0, 3);
next3 = val.substr(3, 3);
last4 = val.substr(6, 4);
if (val.length > 6) {
newValue = first3 + "-" + next3 + "-" + last4;
} else if (val.length > 3) {
newValue = first3 + "-" + next3;
} else if (val.length < 4) {
newValue = first3;
}
} else newValue = val;
setState({ phone: newValue });
for (let i = 0; i < cursorPos.current; ++i) {
if (newValue[i] === "-") {
++cursorPos.current;
}
}
if (newValue[cursorPos.current] === "-" && keyIsDelete.current) {
cursorPos.current++;
}
};
const handleKeyDown = e => {
const allowedKeys = [
"Delete",
"ArrowLeft",
"ArrowRight",
"Backspace",
"Home",
"End",
"Enter",
"Tab"
];
if (e.key === "Delete") {
keyIsDelete.current = true;
} else {
keyIsDelete.current = false;
}
if ("0123456789".includes(e.key) || allowedKeys.includes(e.key)) {
} else {
e.preventDefault();
}
};
useLayoutEffect(() => {
if (inputRef.current) {
inputRef.current.selectionStart = cursorPos.current;
inputRef.current.selectionEnd = cursorPos.current;
}
});
return (
<div className="App">
<input
ref={inputRef}
type="text"
value={state.phone}
placeholder="phone"
onChange={handleChange}
onKeyDown={handleKeyDown}
/>
</div>
);
}
在上面的代码中，这些部分将保存位置：
cursorPos.current = e.target.selectionStart;
let val = e.target.value;
cursorPos.current -= (
val.slice(0, cursorPos.current).match(/-/g) || []
).length;
这些将恢复它：
for (let i = 0; i < cursorPos.current; ++i) {
if (newValue[i] === "-") {
++cursorPos.current;
}
}
还有一个微妙的事情是，通过使用useState({phone:""})我们确保输入会重新渲染，因为它总是设置一个新对象。
CodeSandbox 示例是https://codesandbox.io/s/tel-formating-m1cg2?file=/src/App.js