函数三要素：功能、参数、返回值

1.函数定义和调用

<script>
       //1.定义函数
          function getSum(m) {
              var  sum = 0;
              for(var i = 0;i<= m;i++){
                  sum += i;
              }
              console.log(sum);//55
          }
          //2.调用函数
          getSum(10);
</script>

2.函数返回值

    <script>
         function  getSum(n,m) {
        var sum = 0;
             for(var i = n;i <= m;i++){
                 sum += i;
             }
             return sum;
         }
        console.log(getSum(1,2)); //3
    </script>

3.函数应用

3.1 计算m-n之间的和

<script>
   var Sum1= 0 ;
        //m,n是形参
          function getSum1(m,n) {
              for(var i = m;i<= n ;i++ ){
                  Sum1 +=i;
              }
              console.log(Sum1);
          }
        //实参
          getSum1(1,2); //3
</script>

3.2 求圆的面积

<script>
   function getArea(r) {
         //过滤undefined null "" 0 NaN
           r= r||0;
           var  PI = 3.14;
           return PI *r *r;
       }
       console.log(getArea(4)); //50.24
</script>

3.3 求2个数中的最大值

<script>
       function getMax(a,b) {
            return a>b?a:b;
        }
 console.log( getMax(10,12)); //12
</script>

3.4 求3个数中的最大值

<script>
  function  getMax1(a,b,c) {
            return (a>b?a:b)>c?(a>b?a:b):c;
        }
        console.log(getMax1(1,2,3)); //3
</script>

3.5 求数组中最大的值

<script>
      function  getMax1(a,b,c) {
            return (a>b?a:b)>c?(a>b?a:b):c;
        }
        console.log(getMax1(1,2,3)); //3
</script>

3.6 求数组中最小的值

<script>
     function getArrayMin(array) {
         array = array || [];
         var min = array[0];
         for (var i = 1; i < array.length; i++) {
             if (min > array[i]) {
                 min = array[i];
             }
         }
         return min;
     }
       console.log(getArrayMin([1234,12,11,1,34])); //1
</script>

Snip20170818_1.png

3.7 翻转数组,返回一个新的数组

<script>
   function reverseArray(array) {
           array = array ||[];
          var newArrray = [];
           for(var i = array.length -1;i >=0;i--){
               newArrray[newArrray.length] = array[i];
           }
           return newArrray;
       }
       console.log(reverseArray([1,2,3,4,5]));
</script>

3.8 对数组排序,从小到大

<script>
    //6.对数组排序,从小到大
       function getSort(array) {
             array =  array ||[];
           //a.外层循环,控制趟数
           for(var i = 0 ; i< array.length-1;i++){
                 var isSort = true;
               //b.内层循环,控制比较次数
               for(var j = 0; j<array.length-1-i;j++){
                   //c.判断 比较大小,决定是否交换位置
                   if(array[j]>array[j+1]){

                       var temp = array[j];
                       array[j] = array[j+1];
                       array[j+1] =temp;
                       isSort = false;
                   }
               }
               //d.判断是否已经完成排序
               if (isSort){
                   break;
               }

           }
           //e.返回数组
           return array;
       }
       console.log(getSort([123,456,78,76,5,43]));
</script>

Snip20170818_2.png