检查输入是否已填充答案

【问题标题】：Check if an input is filled or not检查输入是否已填充
【发布时间】：2018-01-29 18:14:41
【问题描述】：

我是 Javascript 的新手，在检查输入是否已填写时遇到问题。

所以问题来了：我有一个标签位于输入上方 (position: absolute)。在焦点和输入被填充时，标签转到输入的顶部。但是如果我删除输入上的文本，标签会留在输入的顶部。

所以我需要检查输入是否已填写，但我的解决方案不起作用。（标签应该回到输入的中心）

任何帮助将不胜感激:)

document.querySelector('.form__input').addEventListener('blur', onInputBlur);

function onInputBlur(ev) {

  if (ev.target && ev.target.value) {
    console.log('is-full');
    ev.target.classList.add('input--filled');
  }

}

/* FORM WRAPPER */

.form__input--wrapper {
  width: 250px;
  position: relative;
  height: 2rem;
  margin: 3rem 0;
}


/* FORM INPUT */

.form__input {
  position: relative;
  background-color: transparent;
  width: 100%;
  margin: 0;
  height: 100%;
  padding: 0;
  border: 0;
  border-bottom: 1px solid deeppink;
  font-size: 15px;
}

.form__input:focus {
  outline: none;
}

.form__input:focus+.form__label,
.input--filled+.form__label {
  top: -100%;
  align-items: flex-end;
  text-transform: uppercase;
  font-size: 11px;
}

.form__input:focus+.form__label::after,
.input--filled+.form__label::after {
  width: 100%;
  bottom: calc(-100% - 0.2rem);
}


/* FORM LABEL */

.form__label {
  position: absolute;
  top: 0;
  left: 0;
  color: #404d5b;
  display: flex;
  align-items: center;
  transition: 0.3s;
  z-index: -1;
  line-height: 1;
  font-family: Raleway;
  font-weight: 500;
  font-size: 15px;
  height: 100%;
  width: 100%;
}

.form__label::after {
  width: 0;
  height: 0.2rem;
  background-color: deeppink;
  position: absolute;
  transition: 0.3s;
  content: '';
  left: 0;
  bottom: -0.2rem;
}

<form class="form-wrapper">

  <div class="form__input--wrapper">
    <input type="text" class="form__input">
    <label for="name" class="form__label" id="a">My awesome label</label>
  </div>

</form>

【问题讨论】：

目前做错了什么？

标签： javascript html css flexbox

【解决方案1】：

如果您的字段为空，则应添加ev.target.classList.remove('input--filled');

document.querySelector('.form__input').addEventListener( 'blur', onInputBlur );

function onInputBlur( ev ) {

	if(ev.target && ev.target.value) {
  	console.log('is-full');
		ev.target.classList.add('input--filled');
	} else {
         ev.target.classList.remove('input--filled');
    }

}

/* FORM WRAPPER */

.form__input--wrapper{
  width: 250px;
  position: relative;
  height: 2rem;
  margin: 3rem 0;
}

/* FORM INPUT */

.form__input{
  position: relative;
  background-color: transparent;
  width: 100%;
  margin: 0;
  height: 100%;
  padding: 0;
  border: 0;
  border-bottom: 1px solid deeppink;
  font-size: 15px;
}

.form__input:focus{
  outline: none;
}

.form__input:focus + .form__label,
.input--filled + .form__label{
  top: -100%;
  align-items: flex-end;
  text-transform: uppercase;
  font-size: 11px;
}

.form__input:focus + .form__label::after, .input--filled + .form__label::after{
  width: 100%;
  bottom: calc(-100% - 0.2rem);
}

/* FORM LABEL */

.form__label{
  position: absolute;
  top: 0;
  left: 0;
  color: #404d5b;
  display: flex;
  align-items: center;
  transition: 0.3s;
  z-index: -1;
  line-height: 1;
  font-family: Raleway;
  font-weight: 500;
  font-size: 15px;
  height: 100%;
  width: 100%;
}

.form__label::after{
  width: 0;
  height: 0.2rem;
  background-color: deeppink;
  position: absolute;
  transition: 0.3s;
  content: '';
  left: 0;
  bottom: -0.2rem;
}

<form class="form-wrapper">

  <div class="form__input--wrapper">
    <input type="text" class="form__input">
    <label for="name" class="form__label" id="a">My awesome label</label>
  </div>
  
</form>

【讨论】：

虽然您的解决方案有效，但值得添加一些细节，说明您为解决 OP 的问题所做的工作

【解决方案2】：

只需再次删除事件侦听器中的类。

document.querySelector('.form__input').addEventListener( 'blur', onInputBlur );

function onInputBlur( ev ) {

	if(ev.target && ev.target.value) {
  	console.log('is-full');
		ev.target.classList.add('input--filled');
	} else {
        console.log('is-empty');
        ev.target.classList.remove('input--filled');
    }

}

/* FORM WRAPPER */

.form__input--wrapper{
  width: 250px;
  position: relative;
  height: 2rem;
  margin: 3rem 0;
}

/* FORM INPUT */

.form__input{
  position: relative;
  background-color: transparent;
  width: 100%;
  margin: 0;
  height: 100%;
  padding: 0;
  border: 0;
  border-bottom: 1px solid deeppink;
  font-size: 15px;
}

.form__input:focus{
  outline: none;
}

.form__input:focus + .form__label,
.input--filled + .form__label{
  top: -100%;
  align-items: flex-end;
  text-transform: uppercase;
  font-size: 11px;
}

.form__input:focus + .form__label::after, .input--filled + .form__label::after{
  width: 100%;
  bottom: calc(-100% - 0.2rem);
}

/* FORM LABEL */

.form__label{
  position: absolute;
  top: 0;
  left: 0;
  color: #404d5b;
  display: flex;
  align-items: center;
  transition: 0.3s;
  z-index: -1;
  line-height: 1;
  font-family: Raleway;
  font-weight: 500;
  font-size: 15px;
  height: 100%;
  width: 100%;
}

.form__label::after{
  width: 0;
  height: 0.2rem;
  background-color: deeppink;
  position: absolute;
  transition: 0.3s;
  content: '';
  left: 0;
  bottom: -0.2rem;
}

<form class="form-wrapper">

  <div class="form__input--wrapper">
    <input type="text" class="form__input">
    <label for="name" class="form__label" id="a">My awesome label</label>
  </div>
  
</form>

【讨论】：

【解决方案3】：

如果输入为 empty，您必须删除该类 - 请参阅下面的演示：

document.querySelector('.form__input').addEventListener('blur', onInputBlur);

function onInputBlur(ev) {

  if (ev.target && ev.target.value.trim().length > 0) {
    ev.target.classList.add('input--filled');
  } else {
    ev.target.classList.remove('input--filled');
  }

}

/* FORM WRAPPER */

.form__input--wrapper {
  width: 250px;
  position: relative;
  height: 2rem;
  margin: 3rem 0;
}


/* FORM INPUT */

.form__input {
  position: relative;
  background-color: transparent;
  width: 100%;
  margin: 0;
  height: 100%;
  padding: 0;
  border: 0;
  border-bottom: 1px solid deeppink;
  font-size: 15px;
}

.form__input:focus {
  outline: none;
}

.form__input:focus+.form__label,
.input--filled+.form__label {
  top: -100%;
  align-items: flex-end;
  text-transform: uppercase;
  font-size: 11px;
}

.form__input:focus+.form__label::after,
.input--filled+.form__label::after {
  width: 100%;
  bottom: calc(-100% - 0.2rem);
}


/* FORM LABEL */

.form__label {
  position: absolute;
  top: 0;
  left: 0;
  color: #404d5b;
  display: flex;
  align-items: center;
  transition: 0.3s;
  z-index: -1;
  line-height: 1;
  font-family: Raleway;
  font-weight: 500;
  font-size: 15px;
  height: 100%;
  width: 100%;
}

.form__label::after {
  width: 0;
  height: 0.2rem;
  background-color: deeppink;
  position: absolute;
  transition: 0.3s;
  content: '';
  left: 0;
  bottom: -0.2rem;
}

<form class="form-wrapper">

  <div class="form__input--wrapper">
    <input type="text" class="form__input">
    <label for="name" class="form__label" id="a">My awesome label</label>
  </div>

</form>

【讨论】：

【解决方案4】：

您需要else 才能删除class

document.querySelector('.form__input').addEventListener( 'blur', onInputBlur );

function onInputBlur( ev ) {

	if(ev.target && ev.target.value) {
  	console.log('is-full');
		ev.target.classList.add('input--filled');
	} else {
    console.log('is-empty');
    ev.target.classList.remove('input--filled');
  }

}

/* FORM WRAPPER */

.form__input--wrapper{
  width: 250px;
  position: relative;
  height: 2rem;
  margin: 3rem 0;
}

/* FORM INPUT */

.form__input{
  position: relative;
  background-color: transparent;
  width: 100%;
  margin: 0;
  height: 100%;
  padding: 0;
  border: 0;
  border-bottom: 1px solid deeppink;
  font-size: 15px;
}

.form__input:focus{
  outline: none;
}

.form__input:focus + .form__label,
.input--filled + .form__label{
  top: -100%;
  align-items: flex-end;
  text-transform: uppercase;
  font-size: 11px;
}

.form__input:focus + .form__label::after, .input--filled + .form__label::after{
  width: 100%;
  bottom: calc(-100% - 0.2rem);
}

/* FORM LABEL */

.form__label{
  position: absolute;
  top: 0;
  left: 0;
  color: #404d5b;
  display: flex;
  align-items: center;
  transition: 0.3s;
  z-index: -1;
  line-height: 1;
  font-family: Raleway;
  font-weight: 500;
  font-size: 15px;
  height: 100%;
  width: 100%;
}

.form__label::after{
  width: 0;
  height: 0.2rem;
  background-color: deeppink;
  position: absolute;
  transition: 0.3s;
  content: '';
  left: 0;
  bottom: -0.2rem;
}

<form class="form-wrapper">

  <div class="form__input--wrapper">
    <input type="text" class="form__input">
    <label for="name" class="form__label" id="a">My awesome label</label>
  </div>
  
</form>

【讨论】：