NaN和任何数值去计算，结果都会输出NaN

    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.         // NaN和任何数值去计算，结果都会输出NaN
    11.         var a ="10";
    12.         var b = 1;
    13.         var c = true;
    14.         console.log(a-b+c);
    15.         console.log(a+b-c);
    16.         console.log(a+c-b);
    17.         //Number(a)-Number(b)+Number(c)；10
    18.         //String(a)+String(b)-Number(c); 100
    19.         //"10true"-1  NaN
    20.     </script>
    21. </body>
    22. </html>