每日思考（2020/08/11）

题目概览

• 用HTML5实现手机摇一摇功能的原理
• 遇到过IE6/7/8/9的BUG及解决方法
• 用js实现一个九九乘法口诀表

题目解答

用HTML5实现手机摇一摇功能的原理

• 原理：以100ms的间隔去扫描加速度计，当检测到加速度发生突变（变化率大于阀值）时，就可以认为此时在甩动手机。由公式可以看到，这里检测的是3个方向的加速度，所以无论往什么方向甩都可以触发摇一摇效果

• 核心代码

  this.deviceMotionHandler = function(eventData) {        
      var acceleration = eventData.acceleration;   
      var curTime = new Date().getTime();         
      //检测频率：每100ms一次
      if ((curTime - that.last_update) > 100) {     
          var diffTime = curTime - that.last_update;      
          that.last_update = curTime;     
          that.x = acceleration.x;            
          that.y = acceleration.y;         
          that.z = acceleration.z;      
          var speed = Math.abs(that.x + that.y + that.z - that.last_x - that.last_y - that.last_z) / diffTime * 10000;            
          if (speed > that.SHAKE_THRESHOLD) {  
              //do something
              that.shakeAudio.play();        //摇一摇音效
              window.navigator.vibrate(200);    //振动效果
              that.shakeEffect.className = 'shake-box shaking';    //摇一摇图片动态
              clearTimeout(shakeTimeout);         
              var shakeTimeout = setTimeout(function() {
                  that.shakeEffect.className = 'shake-box';
              },4000);           
          }    
          that.last_x = that.x;      
          that.last_y = that.y;               
          that.last_z = that.z;         
      }        
  };
  

遇到过IE6/7/8/9的BUG及解决方法

• IE6 IE7 IE8 css bug兼容性解决方法总结归纳
• IE6/7/8/CSS/BUG以及兼容问题解决方法

用js实现一个九九乘法口诀表

/**
 * print 打印乘法表
 * @param {number} length :字符串
 * @return {string}
 */
function print(length) {
    const MAX_WIDTH = 7
    let table = ''
    for (let rhs = 1; rhs <= length; rhs++) {
        for (let lhs = 1; lhs <= length; lhs++) {
            if (lhs <= rhs) table += `${lhs}*${rhs}=${lhs * rhs}`.padEnd(MAX_WIDTH)
        }
        table += '\n'
    }
    return table
}

let reStr = print(9);
console.log(reStr);