我计划有一个输入文本框的前导字符串和零，最大长度为6个前导零。当用户在输入框中键入时，前导零将被擦除，直到它达到最多6个字母。初始字符串是固定的，不能擦除。
例如,
JS000000 //a fixed string (which is the letter 'JS') followed by 6 leading zeros
JS000010 //user has typed the letter '10'
JS123456 //user has typed the letter '123456' and cannot be type further
HTML
<input type="text" name="js" class="form-control" id="js_leading_zero">
JS/jQuery
$('#js_leading_zero').on('keyup', function() {
console.log('i really have no ideas what to do here')
});
正如@rokoc.buljan所建议的，您可以在blur上更改值。一个这样的例子：
null
const inputField = document.getElementById('js_leading_zero')
inputField.addEventListener('blur', updateInput);
function updateInput(e) {
const defaultStr = 'JS000000'
inputField.value = defaultStr.substring(0, defaultStr.length - inputField.value.length) + inputField.value
}<input type="text" name="js" class="form-control" id="js_leading_zero" placeholder="JS000000">