1 <script> 2 "use strict"; 3 var data1 = 0, 4 data2 = "", 5 data3 = false, 6 data4 = undefined, 7 data5 = null; 8 // 下面全部为false 9 console.log(!!data1); 10 console.log(Boolean(data1)); 11 console.log(Boolean(data2)); 12 console.log(Boolean(data3)); 13 console.log(Boolean(data4)); 14 console.log(Boolean(data5)); 15 </script> 16 17 <script> 18 "use strict"; 19 20 var num= "8000"; 21 console.log(num); // "8000" 22 console.log(+num); // 8000 23 console.log(-num); // -8000 24 console.log(num - 100); // 7900 25 console.log(num + 100); // 8000100 26 </script>