觸發原理
原理就是監聽鍵盤輸入,比如掃一個爲6970596130126
的69條形碼,用掃碼槍掃一下會在光標位置依次輸出:
6
9
7
0
5
9
6
1
3
0
2
6
但這不是完整的,所以需要寫一個函數scanEvent
來整理收集到的每個編號。
let code = '';
let lastTime,
nextTime,
lastCode,
nextCode;
function scanEvent(e, cb) {
nextCode = e.which;
nextTime = new Date().getTime();
if (lastCode != null && lastTime != null && nextTime - lastTime <= 30) {
code += String.fromCharCode(lastCode);
} else if (lastCode != null && lastTime != null && nextTime - lastTime > 100) {
code = '';
}
lastCode = nextCode;
lastTime = nextTime;
if (e.which === 13) {
cb(code);
console.log('code', code);
code = '';
}
}
export { scanEvent };
react中的坑
當我們想在willComponentUnMount
階段移除監聽器時,需要傳遞函數名,否則無法移除!!這是非常值得注意的一點。
完整使用
class Sample extends React.Component{
componentDidMount(){
window.addEventListener('keypress', this.scanWrapper, false);
}
componentWillUnmount() {
window.removeEventListener('keypress', this.scanWrapper, false);
}
scanWrapper(e) {
scanEvent(e, (code) => {
// to do something...
});
}
}