原生 JS 实现移动端 Picker 组件-轻识

Picker 是指提供多个选项集合供用户选择其中一项的控件。Picker 展示区域有限，部分选项会被隐藏，最好是当用户对所有选项都比较熟悉、有预期的时候，才使用 Picker。 null

<!DOCTYPE html><html lang="en">  <head>    <meta charset="UTF-8" />    <meta name="viewport" content="width=device-width, initial-scale=1.0" />    <meta http-equiv="X-UA-Compatible" content="ie=edge" />    <title>picker</title>    <style>      * {        margin: 0;        padding: 0;      }      .scroller-component {        display: block;        position: relative;        height: 238px;        overflow: hidden;        width: 100%;      }
      .scroller-content {        position: absolute;        left: 0;        top: 0;        width: 100%;        z-index: 1;      }
      .scroller-mask {        position: absolute;        left: 0;        top: 0;        height: 100%;        margin: 0 auto;        width: 100%;        z-index: 3;        transform: translateZ(0px);        background-image: linear-gradient(            to bottom,            rgba(255, 255, 255, 0.95),            rgba(255, 255, 255, 0.6)          ),          linear-gradient(            to top,            rgba(255, 255, 255, 0.95),            rgba(255, 255, 255, 0.6)          );        background-position: top, bottom;        background-size: 100% 102px;        background-repeat: no-repeat;      }
      .scroller-item {        text-align: center;        font-size: 16px;        height: 34px;        line-height: 34px;        color: #000;      }
      .scroller-indicator {        width: 100%;        height: 34px;        position: absolute;        left: 0;        top: 102px;        z-index: 3;        background-image: linear-gradient(            to bottom,            #d0d0d0,            #d0d0d0,            transparent,            transparent          ),          linear-gradient(to top, #d0d0d0, #d0d0d0, transparent, transparent);        background-position: top, bottom;        background-size: 100% 1px;        background-repeat: no-repeat;      }
      .scroller-item {        line-clamp: 1;        -webkit-line-clamp: 1;        overflow: hidden;        text-overflow: ellipsis;      }</style>  </head>
  <body>    <div class="scroller-component" data-role="component">      <div class="scroller-mask" data-role="mask"></div>      <div class="scroller-indicator" data-role="indicator"></div>      <div class="scroller-content" data-role="content">        <div class="scroller-item" data-value="1">1</div>        <div class="scroller-item" data-value="2">2</div>        <div class="scroller-item" data-value="3">3</div>        <div class="scroller-item" data-value="4">4</div>        <div class="scroller-item" data-value="5">5</div>        <div class="scroller-item" data-value="6">6</div>        <div class="scroller-item" data-value="7">7</div>        <div class="scroller-item" data-value="8">8</div>        <div class="scroller-item" data-value="9">9</div>        <div class="scroller-item" data-value="10">10</div>        <div class="scroller-item" data-value="11">11</div>        <div class="scroller-item" data-value="12">12</div>        <div class="scroller-item" data-value="13">13</div>        <div class="scroller-item" data-value="14">14</div>        <div class="scroller-item" data-value="15">15</div>        <div class="scroller-item" data-value="16">16</div>        <div class="scroller-item" data-value="17">17</div>        <div class="scroller-item" data-value="18">18</div>        <div class="scroller-item" data-value="19">19</div>        <div class="scroller-item" data-value="20">20</div>      </div>    </div>    <script>      let running = {}; // 运行      let counter = 1; // 计时器      let desiredFrames = 60; // 每秒多少帧      let millisecondsPerSecond = 1000; // 每秒的毫秒数
      const Animate = {        // 停止动画        stop(id) {          var cleared = running[id] != null;          if (cleared) {            running[id] = null;          }          return cleared;        },
        // 判断给定的动画是否还在运行        isRunning(id) {          return running[id] != null;        },        start(          stepCallback,          verifyCallback,          completedCallback,          duration,          easingMethod,          root        ) {          let start = Date.now();          let percent = 0; // 百分比          let id = counter++;          let dropCounter = 0;
          let step = function () {            let now = Date.now();
            if (!running[id] || (verifyCallback && !verifyCallback(id))) {              running[id] = null;              completedCallback &&                completedCallback(                  desiredFrames -                    dropCounter / ((now - start) / millisecondsPerSecond),                  id,                  false                );              return;            }
            if (duration) {              percent = (now - start) / duration;              if (percent > 1) {                percent = 1;              }            }            let value = easingMethod ? easingMethod(percent) : percent;            if (percent !== 1 && (!verifyCallback || verifyCallback(id))) {              stepCallback(value);              window.requestAnimationFrame(step);            }          };
          running[id] = true;          window.requestAnimationFrame(step);          return id;        },      };</script>    <script>      let component = document.querySelector("[data-role=component]"); // 插件容器      let content = component.querySelector("[data-role=content]"); // 内容容器      let indicator = component.querySelector("[data-role=indicator]"); // 正确位置实线
      let __startTouchTop = 0;      let __scrollTop = 0;      let __maxScrollTop = component.clientHeight / 2; // 滚动最大值      let __minScrollTop = -(content.offsetHeight - __maxScrollTop); // 滚动最小值      let __isAnimating = false; // 是否开启动画
      let __lastTouchMove = 0; // 最后滚动时间记录      let __positions = []; // 记录位置和时间
      let __deceleratingMove = 0; // 减速运动速度      let __isDecelerating = false; // 是否开启减速状态
      let __itemHeight = parseFloat(window.getComputedStyle(indicator).height);
      // 开始快后来慢的渐变曲线      let easeOutCubic = (pos) => {        return Math.pow(pos - 1, 3) + 1;      };      // 以满足开始和结束的动画      let easeInOutCubic = (pos) => {        if ((pos /= 0.5) < 1) {          return 0.5 * Math.pow(pos, 3);        }        return 0.5 * (Math.pow(pos - 2, 3) + 2);      };      let __callback = (top) => {        const distance = top;        content.style.transform = "translate3d(0, " + distance + "px, 0)";      };      let __publish = (top, animationDuration) => {        if (animationDuration) {          let oldTop = __scrollTop;          let diffTop = top - oldTop;          let wasAnimating = __isAnimating;
          let step = function (percent) {            __scrollTop = oldTop + diffTop * percent;            __callback(__scrollTop);          };          let verify = function (id) {            return __isAnimating === id;          };          let completed = function (            renderedFramesPerSecond,            animationId,            wasFinished) {            if (animationId === __isAnimating) {              __isAnimating = false;            }          };          __isAnimating = Animate.start(            step,            verify,            completed,            animationDuration,            wasAnimating ? easeOutCubic : easeInOutCubic          );        } else {          __scrollTop = top;          __callback(top);        }      };      // 滚动到正确位置的方法      let __scrollTo = (top) => {        top = Math.round((top / __itemHeight).toFixed(5)) * __itemHeight;        let newTop = Math.max(Math.min(__maxScrollTop, top), __minScrollTop);        if (top !== newTop) {          if (newTop >= __maxScrollTop) {            top = newTop - __itemHeight / 2;          } else {            top = newTop + __itemHeight / 2;          }        }        __publish(top, 250);      };      // 开始减速动画      let __startDeceleration = () => {        let step = () => {          let scrollTop = __scrollTop + __deceleratingMove;          let scrollTopFixed = Math.max(            Math.min(__maxScrollTop, scrollTop),            __minScrollTop          ); // 不小于最小值，不大于最大值          if (scrollTopFixed !== scrollTop) {            scrollTop = scrollTopFixed;            __deceleratingMove = 0;          }          if (Math.abs(__deceleratingMove) <= 1) {            if (Math.abs(scrollTop % __itemHeight) < 1) {              __deceleratingMove = 0;            }          } else {            __deceleratingMove *= 0.95;          }          __publish(scrollTop);        };        let minVelocityToKeepDecelerating = 0.5;        let verify = () => {          // 保持减速运行需要多少速度          let shouldContinue =            Math.abs(__deceleratingMove) >= minVelocityToKeepDecelerating;          return shouldContinue;        };        let completed = function (          renderedFramesPerSecond,          animationId,          wasFinished) {          __isDecelerating = false;          if (__scrollTop <= __minScrollTop || __scrollTop >= __maxScrollTop) {            __scrollTo(__scrollTop);            return;          }        };        __isDecelerating = Animate.start(step, verify, completed);      };      let touchStartHandler = (e) => {        e.preventDefault();        const target = e.touches ? e.touches[0] : e;        __startTouchTop = target.pageY;      };      let touchMoveHandler = (e) => {        const target = e.touches ? e.touches[0] : e;        let currentTouchTop = target.pageY;        let moveY = currentTouchTop - __startTouchTop;        let scrollTop = __scrollTop;        scrollTop = scrollTop + moveY;        if (scrollTop > __maxScrollTop || scrollTop < __minScrollTop) {          if (scrollTop > __maxScrollTop) {            scrollTop = __maxScrollTop;          } else {            scrollTop = __minScrollTop;          }        }        if (__positions.length > 40) {          __positions.splice(0, 20);        }        __positions.push(scrollTop, e.timeStamp);
        __publish(scrollTop);
        __startTouchTop = currentTouchTop;        __lastTouchMove = e.timeStamp;      };      let touchEndHandler = (e) => {        if (e.timeStamp - __lastTouchMove < 100) {          // 如果抬起时间和最后移动时间小于 100 证明快速滚动过          let positions = __positions;          let endPos = positions.length - 1;          let startPos = endPos;          // 由于保存的时候位置跟时间都保存了， 所以 i -= 2          // positions[i] > (self.__lastTouchMove - 100) 判断是从什么时候开始的快速滑动          for (            let i = endPos;            i > 0 && positions[i] > __lastTouchMove - 100;            i -= 2          ) {            startPos = i;          }          if (startPos !== endPos) {            // 计算这两点之间的相对运动            let timeOffset = positions[endPos] - positions[startPos]; // 快速开始时间 - 结束滚动时间            let movedTop = __scrollTop - positions[startPos - 1]; // 最终距离 - 快速开始距离            // 基于50ms计算每个渲染步骤的移动            __deceleratingMove = (movedTop / timeOffset) * (1000 / 60); // 移动距离是用分钟来计算的
            let minVelocityToStartDeceleration = 4; // 开始减速的最小速度            // 只有速度大于最小加速速度时才会出现下面的动画            if (Math.abs(__deceleratingMove) > minVelocityToStartDeceleration) {              __startDeceleration();            }          }        }        if (!__isDecelerating) {          __scrollTo(__scrollTop);        }
        __positions.length = 0;      };
      component.addEventListener("touchstart", touchStartHandler);
      component.addEventListener("touchmove", touchMoveHandler);
      component.addEventListener("touchend", touchEndHandler);</script>  </body></html>

Picker 选择器显示一个或多个选项集合的可滚动列表，相比于原生 picker，实现了 iOS 与 Android 端体验的一致性。

要实现横向 picker，其实跟纵向 picker 差不多，都支持滚动时停留在指定位置，并且支持滚动到边界支持反弹效果。

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<!DOCTYPE html><html lang="en">  <head>    <meta charset="UTF-8" />    <meta name="viewport" content="width=device-width, initial-scale=1.0" />    <meta http-equiv="X-UA-Compatible" content="ie=edge" />    <title>picker</title>    <style>      * {        margin: 0;        padding: 0;      }      .scroller-component {        display: block;        position: relative;        height: 34px;        overflow: hidden;        width: 100%;      }
      .scroller-content {        position: absolute;        left: 0;        top: 0;        z-index: 1;        white-space: nowrap;        line-height: 0;        font-size: 0;      }
      .scroller-mask {        position: absolute;        left: 0;        top: 0;        height: 100%;        margin: 0 auto;        width: 100%;        z-index: 3;        transform: translateZ(0px);        background-image: linear-gradient(            to right,            rgba(255, 255, 255, 0.95),            rgba(255, 255, 255, 0.6)          ),          linear-gradient(            to left,            rgba(255, 255, 255, 0.95),            rgba(255, 255, 255, 0.6)          );        background-position: left, right;        background-size: 102px 100%;        background-repeat: no-repeat;      }
      .scroller-item {        text-align: center;        font-size: 16px;        height: 34px;        width: 50px;        line-height: 34px;        color: #000;        display: inline-block;        box-sizing: border-box;      }
      .scroller-indicator {        box-sizing: border-box;        width: 50px;        height: 34px;        position: absolute;        transform: translate3d(-50%, 0, 0);        left: 50%;        top: 0;        z-index: 3;        border: 1px solid red;      }
      .scroller-item {        line-clamp: 1;        -webkit-line-clamp: 1;        overflow: hidden;        text-overflow: ellipsis;      }</style>  </head>
  <body>    <div class="scroller-component" data-role="component">      <div class="scroller-mask" data-role="mask"></div>      <div class="scroller-indicator" data-role="indicator"></div>      <div class="scroller-content" data-role="content">        <div class="scroller-item" data-value="1">1</div>        <div class="scroller-item" data-value="2">2</div>        <div class="scroller-item" data-value="3">3</div>        <div class="scroller-item" data-value="4">4</div>        <div class="scroller-item" data-value="5">5</div>        <div class="scroller-item" data-value="6">6</div>        <div class="scroller-item" data-value="7">7</div>        <div class="scroller-item" data-value="8">8</div>        <div class="scroller-item" data-value="9">9</div>        <div class="scroller-item" data-value="10">10</div>        <div class="scroller-item" data-value="11">11</div>        <div class="scroller-item" data-value="12">12</div>        <div class="scroller-item" data-value="13">13</div>        <div class="scroller-item" data-value="14">14</div>        <div class="scroller-item" data-value="15">15</div>        <div class="scroller-item" data-value="16">16</div>        <div class="scroller-item" data-value="17">17</div>        <div class="scroller-item" data-value="18">18</div>        <div class="scroller-item" data-value="19">19</div>        <div class="scroller-item" data-value="20">20</div>      </div>    </div>    <script>      let running = {}; // 运行      let counter = 1; // 计时器      let desiredFrames = 60; // 每秒多少帧      let millisecondsPerSecond = 1000; // 每秒的毫秒数
      const Animate = {        // 停止动画        stop(id) {          var cleared = running[id] != null;          if (cleared) {            running[id] = null;          }          return cleared;        },
        // 判断给定的动画是否还在运行        isRunning(id) {          return running[id] != null;        },        start(          stepCallback,          verifyCallback,          completedCallback,          duration,          easingMethod,          root        ) {          let start = Date.now();          let percent = 0; // 百分比          let id = counter++;          let dropCounter = 0;
          let step = function () {            let now = Date.now();
            if (!running[id] || (verifyCallback && !verifyCallback(id))) {              running[id] = null;              completedCallback &&                completedCallback(                  desiredFrames -                    dropCounter / ((now - start) / millisecondsPerSecond),                  id,                  false                );              return;            }
            if (duration) {              percent = (now - start) / duration;              if (percent > 1) {                percent = 1;              }            }            let value = easingMethod ? easingMethod(percent) : percent;            if (percent !== 1 && (!verifyCallback || verifyCallback(id))) {              stepCallback(value);              window.requestAnimationFrame(step);            }          };
          running[id] = true;          window.requestAnimationFrame(step);          return id;        },      };</script>    <script>      let component = document.querySelector("[data-role=component]"); // 插件容器      let content = component.querySelector("[data-role=content]"); // 内容容器      let indicator = component.querySelector("[data-role=indicator]"); // 正确位置实线      let __startTouchTop = 0;      let __scrollTop = 0;
      let __isAnimating = false; // 是否开启动画
      let __lastTouchMove = 0; // 最后滚动时间记录      let __positions = []; // 记录位置和时间
      let __deceleratingMove = 0; // 减速运动速度      let __isDecelerating = false; // 是否开启减速状态
      let __itemHeight = parseFloat(window.getComputedStyle(indicator).width);      let __maxScrollTop = __itemHeight / 2; // 滚动最大值      let __minScrollTop = -(content.offsetWidth) + __maxScrollTop; // 滚动最小值
      content.style.left = component.clientWidth / 2 - __itemHeight / 2 + 'px';
      // 开始快后来慢的渐变曲线      let easeOutCubic = (pos) => {        return Math.pow(pos - 1, 3) + 1;      };      // 以满足开始和结束的动画      let easeInOutCubic = (pos) => {        if ((pos /= 0.5) < 1) {          return 0.5 * Math.pow(pos, 3);        }        return 0.5 * (Math.pow(pos - 2, 3) + 2);      };      let __callback = (top) => {        const distance = top;        content.style.transform = "translate3d(" + distance + "px, 0, 0)";      };      let __publish = (top, animationDuration) => {        if (animationDuration) {          let oldTop = __scrollTop;          let diffTop = top - oldTop;          let wasAnimating = __isAnimating;
          let step = function (percent) {            __scrollTop = oldTop + diffTop * percent;            __callback(__scrollTop);          };          let verify = function (id) {            return __isAnimating === id;          };          let completed = function (            renderedFramesPerSecond,            animationId,            wasFinished) {            if (animationId === __isAnimating) {              __isAnimating = false;            }          };          __isAnimating = Animate.start(            step,            verify,            completed,            animationDuration,            wasAnimating ? easeOutCubic : easeInOutCubic          );        } else {          __scrollTop = top;          __callback(top);        }      };      // 滚动到正确位置的方法      let __scrollTo = (top) => {        top = Math.round((top / __itemHeight).toFixed(5)) * __itemHeight;        let newTop = Math.max(Math.min(__maxScrollTop, top), __minScrollTop);        if (top !== newTop) {          if (newTop >= __maxScrollTop) {            top = newTop - __itemHeight / 2;          } else {            top = newTop + __itemHeight / 2;          }        }        __publish(top, 250);      };      // 开始减速动画      let __startDeceleration = () => {        let step = () => {          let scrollTop = __scrollTop + __deceleratingMove;          let scrollTopFixed = Math.max(            Math.min(__maxScrollTop, scrollTop),            __minScrollTop          ); // 不小于最小值，不大于最大值          if (scrollTopFixed !== scrollTop) {            scrollTop = scrollTopFixed;            __deceleratingMove = 0;          }          if (Math.abs(__deceleratingMove) <= 1) {            if (Math.abs(scrollTop % __itemHeight) < 1) {              __deceleratingMove = 0;            }          } else {            __deceleratingMove *= 0.95;          }          __publish(scrollTop);        };        let minVelocityToKeepDecelerating = 0.5;        let verify = () => {          // 保持减速运行需要多少速度          let shouldContinue =            Math.abs(__deceleratingMove) >= minVelocityToKeepDecelerating;          return shouldContinue;        };        let completed = function (          renderedFramesPerSecond,          animationId,          wasFinished) {          __isDecelerating = false;          if (__scrollTop <= __minScrollTop || __scrollTop >= __maxScrollTop) {            __scrollTo(__scrollTop);            return;          }        };        __isDecelerating = Animate.start(step, verify, completed);      };      let touchStartHandler = (e) => {        e.preventDefault();        const target = e.touches ? e.touches[0] : e;        __startTouchTop = target.pageX;      };      let touchMoveHandler = (e) => {        const target = e.touches ? e.touches[0] : e;        let currentTouchTop = target.pageX;        let moveY = currentTouchTop - __startTouchTop;        let scrollTop = __scrollTop;        scrollTop = scrollTop + moveY;        if (scrollTop > __maxScrollTop || scrollTop < __minScrollTop) {          if (scrollTop > __maxScrollTop) {            scrollTop = __maxScrollTop;          } else {            scrollTop = __minScrollTop;          }        }        if (__positions.length > 40) {          __positions.splice(0, 20);        }        __positions.push(scrollTop, e.timeStamp);
        __publish(scrollTop);
        __startTouchTop = currentTouchTop;        __lastTouchMove = e.timeStamp;      };      let touchEndHandler = (e) => {        if (e.timeStamp - __lastTouchMove < 100) {          // 如果抬起时间和最后移动时间小于 100 证明快速滚动过          let positions = __positions;          let endPos = positions.length - 1;          let startPos = endPos;          // 由于保存的时候位置跟时间都保存了， 所以 i -= 2          // positions[i] > (self.__lastTouchMove - 100) 判断是从什么时候开始的快速滑动          for (            let i = endPos;            i > 0 && positions[i] > __lastTouchMove - 100;            i -= 2          ) {            startPos = i;          }          if (startPos !== endPos) {            // 计算这两点之间的相对运动            let timeOffset = positions[endPos] - positions[startPos]; // 快速开始时间 - 结束滚动时间            let movedTop = __scrollTop - positions[startPos - 1]; // 最终距离 - 快速开始距离            // 基于50ms计算每个渲染步骤的移动            __deceleratingMove = (movedTop / timeOffset) * (1000 / 60); // 移动距离是用分钟来计算的
            let minVelocityToStartDeceleration = 4; // 开始减速的最小速度            // 只有速度大于最小加速速度时才会出现下面的动画            if (Math.abs(__deceleratingMove) > minVelocityToStartDeceleration) {              __startDeceleration();            }          }        }        if (!__isDecelerating) {          __scrollTo(__scrollTop);        }
        __positions.length = 0;      };
      component.addEventListener("touchstart", touchStartHandler);
      component.addEventListener("touchmove", touchMoveHandler);
      component.addEventListener("touchend", touchEndHandler);</script>  </body></html>