数学函数

Math.random()

• 随机天生0到1的小数,包含0,不包含1

  <script>
      console.log(Math.random());     // 0.731681187341011
  </script>
  

Math.ceil()

• 返回大于参数值的最小整数(天花板值),碰到小数向上取整

  <script>
      console.log(Math.ceil(0.0));    // 0
      console.log(Math.ceil(-0.0));   // -0
      console.log(0 === -0);          // true
      console.log(Math.ceil(2.3));    // 3
      console.log(Math.ceil(-1.5));   // -1
  </script>
  

Math.floor()

• 返回小于参数值的最大整数(地板值),碰到小数向下取整

  <script>
      console.log(Math.floor(0.0));    // 0
      console.log(Math.floor(-0.0));   // -0
      console.log(0 === -0);           // true
      console.log(Math.floor(2.3));    // 2
      console.log(Math.floor(-1.5));   // -2
  </script>     
  

Math.round()

• 四舍五入返回整数

  <script>
      console.log(Math.round(0.49));      // 0
      console.log(Math.round(-0.49));     // -0  
  </script> 
  

Math.max()

• 返回最大值

  <script>
      let arr = [0.2, 0.32, 12];
      console.log(Math.max(arr));       // NaN
      console.log(Math.max(0.49, 0.231, 932));      // 932
      console.log(Math.max(0,-0));     // 0  
  </script>   
  

Math.min()

• 返回最小值

  <script>
      let arr = [0.2, 0.32, 12];
      console.log(Math.min(arr));       // NaN
      console.log(Math.min(0.49, 0.231, 932));      // 0.231
      console.log(Math.min(0,-0));     // -0  
  </script>
  

案例一

• 恣意局限的随机整数天生函数

  <script>
      // 恣意局限的随机整数天生函数
      function getIntRadom(min, max){
          let x = Math.random() * (max - min + 1) + min;  // [0,1)*5 + 2 -> [0,5) + 2 -> [2,7)
          return Math.floor(x);                           // [2,7) -> [2,6]         
      }
      console.log(getIntRadom(2,6));
  </script> 
  

案例二

• 返回数值的整数部份

  <script>
      // 返回数值的整数部份
      function getInt(x){
         x = Number(x);
         return x < 0 ? Math.ceil(x) : Math.floor(x);
     }
     console.log(getInt(7.78));      // 7
  </script>
  

案例三

• 返回数值的整数部份

  <script>
      function random_vlidateCode(x){
          let str1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
              // str1 += "abcdefghijklmnopqrst";
              str1 += str1.toLowerCase();
              str1 += "0123456789";
          let str = "";
          for(let i = 0; i < x; i++){
              let vlidateCode = Math.floor(Math.random() * str1.length);                
              str += str1.substring(vlidateCode, vlidateCode + 1);                
          }
          return str;
      }
      console.log(random_vlidateCode(4)); // 天生四位随机数
  </script>