当文本扩展到输入时，输入字体的渐变透明度

Question

我遇到了一个问题：我正在创建一些具有不同状态的输入;其中一种状态是当输入文本比输入本身更长时：在这种情况下，隐藏在输入左侧的文本应该以渐变透明度淡出：

我现在的代码是这样的：

.Input {
    position: relative;
    width: 100%;
    border: none; 
    width: 200px;
}

.Input:before {
    content: '';
    position: absolute;
    bottom: 0;
    width: 100%;
    transition: border-bottom 0.5s ease;
    border-bottom: 1px solid gainsboro;
}

.Input input {
    margin-top: 20px;
    height: 40px;
    width: 100%;
    padding-left: 0;
    font-size: 16px;
    font-weight: 300;
    background-color: transparent;
    background-image: linear-gradient(to bottom, gainsboro 50%, tomato 50%);
    background-repeat: no-repeat;
    background-size: 0 11%;
    background-position: 50% 100%;
    transition: all 0.5s ease;
    box-shadow: none;
}

.Input h1 {
    font-size: 16px;
    color: gainsboro;
    font-weight: 400;
    position: absolute;
    pointer-events: none;
    left: 0;
    bottom: 0;
    transition: 0.5s ease all;
    width: 100%;
    line-height: unset;
}

.Input:hover:before {
    transition: border-bottom 0.5s ease;
    border-bottom: 1px solid dimgray;
}

input:focus {
    background-color: transparent;
    background-image: linear-gradient(to bottom, transparent 50%, tomato 50%);
    background-repeat: no-repeat;
    background-size: 100% 11%;
    background-position: 50% 100%;
    transition: all 0.5s ease;
}

input:focus,
input:not(:focus):valid {
    border: none;
    outline: none;
}

input:focus ~ h1, input:not(:focus):valid ~ h1 {
    color: tomato;
    transition: all 0.5s ease;
    transform: translateY(-25px);
}

<div class="Input">
<input type="text" class="Input" name="testInput" value="" data-id="" required>
<h1>
MyInput
</h1>
</div>
<br>

欢迎任何帮助......

提前致谢！

Answer 1

检查文本是否达到特定长度的想法，如果是，则显示隐藏元素。

在下面的示例中，我简化为测试，但您需要做的是计算文本应采用的宽度，然后与输入宽度进行比较。你可以查看这个链接，了解一些想法Calculating text width

$('.Input input').on('keypress change keyup', function() {
  if ($(this).val().length > 10) {
    $(this).parent().find('.grad').css('opacity', '1');
  } else {
    $(this).parent().find('.grad').css('opacity', '0');
  }
})
$('.Input .grad').click(function() {
  $(this).parent().find('input').focus();
}) 

.Input {
  position: relative;
  width: 100%;
  border: none;
  width: 200px;
}

.grad {
  position: absolute;
  cursor: text;
  top: 25px;
  bottom: 2px;
  left: 0;
  right: 90%;
  opacity: 0;
  transition: 0.5s;
  z-index: 1;
  background-image: linear-gradient(to right, rgba(255, 255, 255, 0.8), transparent);
}
.Input:before {
  content: '';
  position: absolute;
  bottom: 0;
  width: 100%;
  transition: border-bottom 0.5s ease;
  border-bottom: 1px solid gainsboro;
}

.Input input {
  margin-top: 20px;
  height: 40px;
  width: 100%;
  padding-left: 0;
  font-size: 16px;
  font-weight: 300;
  background-color: transparent;
  background-image: linear-gradient(to bottom, gainsboro 50%, tomato 50%);
  background-repeat: no-repeat;
  background-size: 0 11%;
  background-position: 50% 100%;
  transition: all 0.5s ease;
  box-shadow: none;
}

.Input h1 {
  font-size: 16px;
  color: gainsboro;
  font-weight: 400;
  position: absolute;
  pointer-events: none;
  left: 0;
  bottom: 0;
  transition: 0.5s ease all;
  width: 100%;
  line-height: unset;
}

.Input:hover:before {
  transition: border-bottom 0.5s ease;
  border-bottom: 1px solid dimgray;
}

input:focus {
  background-color: transparent;
  background-image: linear-gradient(to bottom, transparent 50%, tomato 50%);
  background-repeat: no-repeat;
  background-size: 100% 11%;
  background-position: 50% 100%;
  transition: all 0.5s ease;
}

input:focus,
input:not(:focus):valid {
  border: none;
  outline: none;
}

input:focus~h1,
input:not(:focus):valid~h1 {
  color: tomato;
  transition: all 0.5s ease;
  transform: translateY(-25px);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="Input">
  <span class="grad"></span>
  <input type="text" class="Input" name="testInput" value="" data-id="" required>
  <h1>
    MyInput
  </h1>
</div>
<br>