1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title></title> 6 <script type="text/javascript"> 7 function test(){ 8 var obj={name:"哈喽"}; 9 var t1=!!obj.name;//等效于var test=o.flag||false; 10 console.log(t1);//true 11 var t2=obj.name||false; 12 console.log(t2);//哈喽 13 14 var obj1={name:""}; 15 var t3 = obj1.name||false; 16 console.log((!!obj1.name)+""+t3);//false 17 18 var obj2={name:undefined}; 19 var t4 = obj2.name||false; 20 console.log((!!obj2.name)+""+t4);//false 21 22 var obj3={name:null}; 23 var t5 = obj3.name||false; 24 console.log((!!obj3.name)+""+t5);//false 25 26 var obj4={name:" "}; 27 var t6 = obj4.name||false; 28 console.log((!!obj4.name)+""+t6);//true 空格 29 30 var obj5={}; 31 console.log(!!obj5.name);//false 32 33 var obj6; 34 console.log(!!obj6);//false 35 36 var obj7=''; 37 console.log(!!obj7);//false 38 39 var obj8=' '; 40 console.log(!!obj8);//true 41 42 var obj9=undefined; 43 console.log(!!obj9);//false 44 45 var obj10=null; 46 console.log(!!obj10);//false 47 } 48 function isSupportHistoryPushState(){ 49 console.log(!!(window.history && history.pushState));// 50 return !!(window.history && history.pushState);//返回true or false 51 } 52 </script> 53 </head> 54 <body> 55 <input type="button" onclick="test();" value="test!!的使用方式"/> 56 <input type="button" onclick="isSupportHistoryPushState();" value="判断浏览器是否支持history.pushState"/> 57 </body> 58 </html>