手机号3-4-5

$('#m-input').on('keyup', function () {
    var that = $(this);
    var value = that.val();
    value = value.replace(/[^0-9]/ig, ""); 
    var arr = value.split('');
    if (arr.length >= 4) {
      arr.splice(3, 0, ' ');
    } 
    if (arr.length >= 9) {
      arr.splice(8, 0, ' ');
    }
    value = arr.join('');
    that.val(value);
});