javascript - 设置无法删除的默认文本框值

Question

文本框的所有值均以 T- 开头

如何在文本框中预填充 T-，而用户无法删除 T-

感谢您的帮助

Answer 1

试试这个

<input id="field" type="text" value="T-" size="50" />

JS

var readOnlyLength = $('#field').val().length;

 $('#output').text(readOnlyLength);

$('#field').on('keypress, keydown', function(event) {
    var $field = $(this);
    $('#output').text(event.which + '-' + this.selectionStart);
    if ((event.which != 37 && (event.which != 39))
        && ((this.selectionStart < readOnlyLength)
        || ((this.selectionStart == readOnlyLength) && (event.which == 8)))) {
        return false;
    }
});  

DEMO