js 实现验证码输入框示例详解

<div class="box">
    <div class="field-list">
        <div class="field-item"></div>
        <div class="field-item"></div>
        <div class="field-item"></div>
        <div class="field-item"></div>
        <div class="field-item"></div>
        <div class="field-item"></div>
    </div>
    <input class="field-input" type="text" maxlength="6">
</div>

.box {
    position: relative;
    width: 338px;
    overflow: hidden;
}
.field-list {
    display: flex;
    justify-content: space-between;
}
.field-item {
    box-sizing: border-box;
    width: 48px;
    height: 48px;
    line-height: 46px;
    font-size: 24px;
    text-align: center;
    font-weight: bold;
    border: 1px solid #ccc;
    border-radius: 3px;
}
.field-item-focus {
    border-color: #409EFF;
}
.field-item-focus::before {
    content: '';
    display: block;
    width: 2px;
    height: 30px;
    margin: 8px auto;
    background: skyblue;
    animation: blink 1s steps(1) infinite;
}
@keyframes blink {
    50% {
        opacity: 0;
    }
}
.field-input {
    box-sizing: border-box;
    position: absolute;
    top: 0;
    right: 0;
    width: calc(100% + 60px);
    height: 48px;
    padding: 0;
    border: none;
    outline: none;
    opacity: 0;
    background: transparent;
}

// 获取dom
const fieldList = document.querySelectorAll('.field-item');
const fieldInput = document.querySelector('.field-input');
// 监听input输入事件，只支持输入数字，过滤非数字字符
fieldInput.addEventListener('input', function (e) {
    const v = e.target.value.replace(/[^\d]/g, '');
    e.target.value = v;
    // 考虑粘贴情况，循环赋值
    for (let i = 0; i < 6; i++) {
        fieldList[i].innerHTML = v[i] || '';
    }
    // 移除旧光标
    removeCursor();
    // 计算新光标出现位置
    calcCursorPosition();
});
// focus
fieldInput.addEventListener('focus', function (e) {
    calcCursorPosition();
});
// blur
fieldInput.addEventListener('blur', function (e) {
    removeCursor();
});
// 计算光标出现位置
function calcCursorPosition() {
    const length = fieldInput.value.length;
    if (length < 6) {
        fieldList[length].classList.add('field-item-focus');
    }
}
// 移除光标
function removeCursor() {
    // 最后一位没有光标，?.操作符避免报错
    document.querySelector('.field-item-focus')?.classList.remove('field-item-focus');
}