1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
    6.     <title>Document</title>
    7. </head>
    8. <body>
    9.     <script>
    10.         var arr = [1,2,3,4];
    11.         var sum = 0;
    12.         for(var i=0;i<arr.length;i++){
    13.             sum =sum+ arr[i];
    14.         }
    15.         //sum=1
    16.         //sum=1+2;
    17.         //sum =3+3;
    18.         //sum =6+4
    19.         console.log(sum)
    20.     </script>
    21. </body>
    22. </html>

    1.PNG