馃コ娆㈣繋鏈夊叴瓒ｇ殑鏈嬪弸锛屼竴璧锋潵鍋氱偣鏈夋剰涔夌殑浜嬪惂锛佹湰鏂囪瘧鑰咃細chressYu鎴戞帹鍑轰簡涓€涓瘡鍛ㄧ炕璇戦」鐩紝浠撳簱鍦板潃锛岃闂湴鍧€杩樻槸寰堢己蹇楀悓閬撳悎鐨勬湅鍙嬶紝绾睘涓汉鍏磋叮锛屽綋鐒朵篃鏈夊姪浜庢彁楂樿嫳璇拰鍓嶇鎶€鑳斤紝瑕佹眰锛氳嫳璇笉宸璋憋紝鐔熺粌浣跨敤github锛屾墽鐫€锛岃唉閫婏紝瀵硅嚜宸辨墍鍋氱殑浜嬭礋璐ｃ€傛兂鍙備笌鐨勬湅鍙嬪彲浠ョ淇x鎴栬€呯粰浠撳簱鍙慽ssue娑堟伅銆傛垜鐨勫崥瀹篃鏈夊叿浣撶殑涓汉鑱旂郴鏂瑰紡锛歞aodaolee.cn澶у鏁扮紪绋嬭瑷€閮芥湁鈥滅┖鍊尖€濈殑瀹氫箟锛屼篃灏辨槸null銆傚畠琛ㄧず璇ュ彉閲忓綋鍓嶆湭鎸囧悜瀵硅薄鈥斺€斾緥濡傦紝褰撳畠灏氭湭鍒濆鍖栨椂銆備笌鍏朵粬璇█鐩告瘮锛孞avaScript鍖呭惈涓や釜杩欐牱鐨勭┖鍊硷細undefined鍜宯ull銆傚湪鏈枃涓紝鎴戜滑灏嗘帰璁ㄥ畠浠箣闂寸殑宸紓锛屼互鍙婂浣曟渶濂藉湴浣跨敤鎴栭伩鍏嶅畠浠€倁ndefined鍜宯ull杩欎袱涓€奸潪甯哥浉浼硷紝鍙互浜掓崲浣跨敤銆傛墍浠ヤ粬浠殑鍖哄埆闈炲父寰銆侲CMAScript涓璾ndefined鍜宯ull鐨勫畾涔夛細ECMAScript涓璾ndefined鍜宯ull鐨勫畾涔夊涓嬶細undefined锛氬綋涓€涓彉閲忔病鏈夎璧嬪€兼椂銆俷ull锛氫笉浠ｈ〃浠讳綍瀵硅薄锛涚◢鍚庢垜浠皢鐪嬪埌浣滀负绋嬪簭鍛樺浣曟渶濂藉湴澶勭悊杩欎袱涓€笺€備袱涓┖鍊?涓€涓笉鍙垹闄ょ殑閿欒鍏锋湁涓や釜绌哄€肩殑Javascript鐩村埌鐜板湪閮借璁や负鏄竴涓碂绯曠殑璁捐锛堝嵆浣挎槸JavaScript鐨勫垱寤鸿€匓rendanEich锛夈€傞偅涔堜负浠€涔堜笉浠庝腑鍒犻櫎涓€涓憿锛烰avaScript鐨勬牳蹇冨師鍒欐槸姘镐笉鐮村潖鍚戝悗鍏煎鎬с€傝繖涓師鍒欐湁寰堝濂藉銆備絾瀹冩渶澶х殑缂虹偣鏄笉鑳藉幓闄ら敊璇殑璁捐銆倁ndefined鍜宯ull鐨勫巻鍙插湪Java涓紙瀵笿avaScript鏈夊緢澶氬惎鍙戯級锛屽垵濮嬪寲鍊煎彇鍐充簬鍙橀噺鐨勯潤鎬佺被鍨嬶細鍒濆鍖栨椂鍖呭惈null瀵硅薄銆備换浣曞熀纭€绫诲瀷閮藉寘鍚畠鍒濆鍖栫殑鍊笺€備緥濡傦細int绫诲瀷琚垵濮嬪寲涓?銆傚湪JavaScript涓紝姣忎釜鍙橀噺閮藉彲浠ュ寘鍚璞″€煎拰榛樿鍊笺€傚洜姝わ紝濡傛灉null琛ㄧず鈥滀笉鏄璞♀€濓紝鍒橨avaScript闇€瑕佷竴涓〃绀衡€滄棦涓嶆槸瀵硅薄涔熶笉鏄垵濮嬪寲鍊尖€濈殑鍒濆鍊笺€傝鍩哄€兼湭瀹氫箟銆倁ndefined鏄浣曚骇鐢熺殑濡傛灉涓€涓彉閲弇yVar娌℃湁鍒濆鍖栦竴涓€硷紝閭ｄ箞瀹冪殑鍊煎氨鏄痷ndefined锛歭etmyVar;assert.equal(myVar,undefined);濡傛灉瀵硅薄涓病鏈塽nknownProp灞炴€э紝璁块棶璇ュ睘鎬ф椂浼氫骇鐢焨ndefined:constobj={};assert.equal(obj.unknownProp,undefined);濡傛灉涓€涓嚱鏁版病鏈夋槑纭殑杩斿洖鍊硷紝閭ｄ箞杩欎釜鍑芥暟灏变細杩斿洖undefined锛歠unctionmyFunc(){}assert.equal(myFunc(),undefined);濡傛灉涓€涓嚱鏁扮殑杩斿洖娌℃湁杩斿洖浠讳綍鍊硷紝閭ｄ箞浠栧氨浼氳繑鍥炴湭瀹氫箟锛氬嚱鏁癿yFunc(){return;}assert.equal(myFunc(),undefined);濡傛灉鍑芥暟鐨勫舰鍙倄鍦ㄨ皟鐢ㄦ椂琚渷鐣ワ紝閭ｄ箞瀹冨氨鏄湭瀹氫箟鐨勶細functionmyFunc(x){assert.equal(x,undefined);}myFunc();濡傛灉涓€涓彉閲忔槸undefined鎴杗ull锛屽綋鐢╟hain:undefined?璋冪敤ojb?someProp鏃跺畠浼氳繑鍥瀠ndefined锛?someProp//undefinednull?.someProp//undefinednull鏄浣曚骇鐢熺殑瀵硅薄鐨勫師鍨嬭涔堟槸瀵硅薄锛岃涔堟槸鍘熷瀷閾炬湯灏剧殑null銆侾rototype娌℃湁鍘熷瀷锛歄bject.getPrototypeOf(Object.prototype)//null濡傛灉鎴戜滑浼犻€掍竴涓鍒欒〃杈惧紡/a/锛屼娇鐢ㄨ繖涓鍒欒〃杈惧紡鏉ュ尮閰嶅瓧绗︿覆'x'锛屽鏋滃尮閰嶅け璐ワ紝瀹冧細杩斿洖涓€涓猲ull锛?a/.exec('x')//null璋冪敤JSON.stringify鏃讹紝JSON鍙敮鎸乶ull锛屼笉鏀寔undefinedJSON.stringify({a:undefined,b:null})//'{"b":null}'undefined鍜宯ullundefined浠ュ強鍙傛暟榛樿鍊煎浣曞鐞嗗弬鏁伴粯璁ゅ€肩敤浜庯細鍙傛暟缂哄け鏃讹紝鍏ュ弬鏈畾涔変緥濡傦細functionmyFunc(arg='abc'){returnarg;}assert.equal(myFunc('hello'),'hello');assert.equal(myFunc(),'abc');assert.equal(myFunc(undefined),'abc');undefined涔熷彲浠ヨЕ鍙戝舰寮忓弬鏁颁娇鐢ㄩ粯璁ゅ€笺€備互涓嬬ず渚嬫樉绀轰簡瀹冪殑鐢ㄥ锛歠unctionconcat(str1='',str2=''){returnstr1+str2;}functiontwice(str){//(A)returnconcat(str,str);}鍦ˋ琛屼腑锛屾垜浠病鏈変负str鎸囧畾鍙傛暟榛樿鍊笺€傚綋缂哄皯姝ゅ弬鏁版椂锛宼wice鍑芥暟灏嗕娇鐢ㄩ粯璁ゅ€笺€倁ndefined鍜宒estructuringdefaultvalues鍦ㄨВ鏋勬椂琚祴浜堢被浼间簬鍑芥暟榛樿鍊肩殑榛樿鍊笺€傚鏋滃彉閲忓湪瑙ｆ瀯杩囩▼涓病鏈夊尮閰嶅埌鎴栬€呭尮閰嶅埌undefined锛岄偅涔堝畠浼氶噰鐢ㄩ粯璁ゅ€硷細const[a='a']=[];assert.equal(a,'a');const[b='b']=[undefined];assert.equal(b,'b');const{prop:c='c'}={};assert.equal(c,'c');const{prop:d='d'}={prop:undefined};assert.equal(d,'d');undefined,null鍜宱ptionalchaining褰撲娇鐢∣ptional閾炬帴value?.prop鏃讹細濡傛灉value鏄痷ndefined鎴杗ull锛屽垯杩斿洖undefined锛岃繖鏄痸alue.prop鎶涘嚭寮傚父鏃跺彂鐢熺殑鎯呭喌銆傚惁鍒欙紝杩斿洖value.prop銆俧unctiongetProp(value){//鍙€夌殑闈欐€佸睘鎬ц闂繑鍥炲€?.prop;}assert.equal(getProp({prop:123}),123);assert.equal(getProp(undefined),undefined);assert.equal锛坓etProp锛堢┖锛夛紝鏈畾涔夛級锛涗互涓嬫搷浣滅被浼硷細obj?.[芦expr禄]//鍙€夊姩鎬佸睘鎬ccessfunc?.(芦arg0禄,芦arg1禄)//鍙€夊嚱鏁版垨鏂规硶璋冪敤undefined,null鍜岀┖鍚堝苟杩愮畻绗henullmergeroperator锛燂紵灏辨槸璁╂垜浠湪閬囧埌undefined鍜宯ull鐨勬椂鍊欎娇鐢ㄩ粯璁ゅ€硷細undefined??'榛樿鍊?//'榛樿鍊?null??'榛樿鍊?//'榛樿鍊?0??'榛樿鍊?//0123??'榛樿鍊?//123''??'榛樿鍊?//'''abc'??'defaultvalue'//'abc'logicalemptyAssignment??=灏唍ullconsolidator鍜宎ssignment缁勫悎鍦ㄤ竴璧凤細functionsetName(obj){obj.name??='(Unnamed)';returnobj;}assert.deepEqual(setName({}),{name:'(Unnamed)'});assert.deepEqual(setName({name:undefined}),{name:'(Unnamed)'});assert.deepEqual(setName({name:null}),{name:'(Unnamed)'});assert.deepEqual(setName({name:'Jane'}),{name:'Jane'});濡備綍澶勭悊null鍜寀ndefined涓嬮潰鍑犺妭璁茶В濡備綍鍦ㄦ垜浠嚜宸辩殑浠ｇ爜涓鐞唘ndefined鍜寀ndefinednull鏈€甯哥敤鐨勬柟娉曟棦涓嶆槸鏈畾涔夌殑锛屼篃涓嶆槸浣滀负瀹為檯鍊肩殑null銆備緥濡傦紝鎴戜滑鍙兘甯屾湜灞炴€ile.title濮嬬粓瀛樺湪骞朵笖濮嬬粓鏄竴涓瓧绗︿覆銆傛湁涓ょ甯歌鐨勬柟娉曞彲浠ュ疄鐜拌繖涓€鐐广€傝娉ㄦ剰锛屽湪杩欑瘒鍗氭枃涓紝鎴戜滑鍙€冭檻undefined鍜宯ull锛岃€屼笉鑰冭檻鍊兼槸鍚︿负瀛楃涓层€傛偍蹇呴』鑷鍐冲畾鏄惁灏嗘浣滀负闄勫姞瀹夊叏鎺柦瀹炴柦銆倁ndefined鍜宯ull閮借绂佹銆備緥濡傦細functioncreateFile(title){if(title===undefined||title===null){thrownewError('`title`涓嶈兘涓虹┖');}//路路路}涓轰粈涔堥€夋嫨杩欑鏂瑰紡锛熸垜浠笇鏈涘悓浜嬪鐞唘ndefined鍜宯ull锛屾墍浠ユ垜浠粡甯歌繖鏍峰啓锛屼緥濡傦細//Detectingifapropertyexistsif(!obj.requiredProp){obj.requiredProp=123;}//DefaultvaluesvianullishcoalescingoperatorconstmyValue=myParameter?锛?涓€浜涢粯璁?;濡傛灉鎴戜滑鐨勪唬鐮佸洜涓簎ndefined鍜宯ull瀵艰嚧浜嗕竴浜涢棶棰橈紝鎴戜滑甯屾湜浠栧敖蹇姏鍑恒€傚綋閬囧埌undefined鍜宯ull鏃讹紝瑙﹀彂榛樿鍊笺€備緥濡傦細functioncreateFile(title){title??='(Untitled)';//路路路}鎴戜滑杩欓噷涓嶈兘浣跨敤鍑芥暟鐨勯粯璁ゅ€硷紝鍥犱负瀹冨彧鑳界敱undefined瑙﹀彂锛屾墍浠ユ垜浠繖閲屼娇鐢ㄧ┖鍊糓ergeoperator??=涓轰粈涔堣閫夋嫨杩欑鏂瑰紡鍛紵鎴戜滑甯屾湜瀵箄ndefined鍜宯ull鐨勫鐞嗕繚鎸佷竴鑷淬€傛垜浠笇鏈涙垜浠殑浠ｇ爜鑳藉鍑嗙‘鍦板鐞唘ndefined鍜宯ull銆傛湭瀹氫箟鎴杗ull琛ㄧず绌哄€笺€備緥濡傦紝鎴戜滑鍙兘甯屾湜灞炴€ile.title鏄竴涓瓧绗︿覆鎴栦竴涓┖鍊硷紙鏂囦欢娌℃湁title灞炴€э級銆傛湁鍑犵鏂规硶鍙互瀹炵幇杩欎竴鐐广€傝繖閲宯ull鐢ㄤ簬琛ㄧず绌哄€笺€備緥濡傦細functioncreateFile(title){if(title===undefined){thrownewError(''title'mustnotbeundefined');}return{title};}鎴杣ndefined瑙﹀彂榛樿鍊硷細functioncreateFile(title='(Untitled)'){return{title};}涓轰粈涔堥€夋嫨杩欑鏂瑰紡锛氭垜浠渶瑕佷竴涓┖鍊兼潵琛ㄧず娌℃湁鎴戜滑涓嶆兂瑕乶ull瑙﹀彂鍙傛暟榛樿鍊煎拰瑙ｆ瀯榛樿鍊笺€傛垜浠笇鏈涘皢绌哄€煎瓧绗︿覆鍖栦负JSON锛堝洜姝や笉鑳戒娇鐢╱ndefined锛夈€倁ndefined琛ㄧず涓€涓┖鍊间緥濡傦細functioncreateFile(title){if(title===null){thrownewError('`title`mustnotbenull');}return{title};}涓轰粈涔堥€夋嫨杩欑鏂瑰紡锛氭垜浠渶瑕佷竴涓┖鍊兼潵琛ㄧず鍚︼紝鎴戜滑纭疄甯屾湜绌哄€艰Е鍙戝弬鏁伴粯璁ゅ€煎拰瑙ｆ瀯榛樿鍊笺€倁ndefined鐨勪竴涓己鐐规槸瀹冮€氬父鏄敱JavaScript鏃犳剰鍒涘缓鐨勶細鐢辨湭鍒濆鍖栫殑鍙橀噺銆佸睘鎬у悕绉颁腑鐨勬嫾鍐欓敊璇€佸繕璁颁粠鍑芥暟杩斿洖鏌愪簺鍐呭绛夈€備负浠€涔堜笉鑳藉悓鏃朵娇鐢╱ndefined鍜宯ull锛熷綋鏀跺埌涓€涓€兼椂锛屽皢undefined鍜宯ull閮借涓衡€滅┖鍊尖€濇槸鏈夋剰涔夌殑銆傚洜涓猴紝褰撴垜浠垱寤轰竴涓€肩殑鏃跺€欙紝鎴戜滑甯屾湜鏄樉寮忕殑锛岃繖鏍锋垜浠彲浠ユ柟渚垮湴澶勭悊杩欎釜鍊笺€傚綋鎴戜滑涓嶆兂浣跨敤undefined鎴杗ull鏉ヨ〃绀虹┖鍊兼椂锛屾垜浠簲璇ユ€庝箞鍋氬憿锛熻寰€涓嬬湅锛佽〃绀虹┖鍊肩殑鍏朵粬鏂瑰紡鐗瑰埆鏄竴涓€兼垜浠彲浠ュ垱寤轰竴涓壒娈婄殑鍊兼潵琛ㄧず.title涓虹┖锛歝onstUNTITLED=Symbol('UNTITLED');const鏂囦欢={鏍囬锛氭棤鏍囬锛寎锛沞mptyobjectpatternempty瀵硅薄妯″紡鏉ヨ嚜闈㈠悜瀵硅薄缂栫▼锛氬叕鍏辩被閮界户鎵跨浉鍚岀殑鎺ュ彛銆傛瘡涓瓙绫诲疄鐜板疄渚嬭繍琛岀殑涓嶅悓妯″紡銆傚叾涓竴绉嶆ā寮忔槸鈥滅┖鈥濄€傚湪涓嬮潰鐨勭ず渚嬩腑锛孶ntitledFile瀹炵幇浜嗏€渘ull鈥濇ā寮忋€?/鎶借薄瓒呯被File{constructor(content){if(new.target===File){thrownewError('涓嶈兘瀹炰緥鍖栬繖涓被');}this.content=鍐呭锛泒}classTitledFileextendsFile{constructor(content,title){super(content);this.title=鏍囬锛泒getTitle(){杩斿洖杩欎釜鏍囬锛泒}classUntitledFileextendsFile{constructor(content){super(content);}getTitle(){return'(Untitled)';}}constfiles=[newTitledFile('浜茬埍鐨勬棩璁帮紒','鎴戠殑鏃ヨ'),newUntitledFile('鎻愰啋锛氶€夋嫨涓€涓爣棰橈紒'),];assert.deepEqual(files.map(f=>f.getTitle()),['鎴戠殑鏃ヨ','(鏃犻)',]);鎴戜滑涔熷彲浠ュ彧浣跨敤绌哄璞℃ā寮廎ile鏉ュ鐞唗itle灞炴€э紙鑰屼笉鏄鐞嗘暣涓枃浠跺璞★級銆傚彲鑳界殑绫诲瀷鍐欏嚭鎵€鏈夊彲鑳界殑绫诲瀷鏉ュ鐞嗛棶棰橈細functiongetTitle(file){switch(file.title.kind){case'just':returnfile.title.value;case'nothing':return'(Untitled)';榛樿鍊硷細鎶涘嚭鏂扮殑閿欒锛堬級锛泒}constfiles=[{title:{kind:'just',value:'MyDiary'},content:'浜茬埍鐨勬棩璁帮紒',},{title:{kind:'nothing'},content:'鎻愰啋锛氶€夋嫨涓€涓爣棰橈紒',},];assert.deepEqual(files.map(f=>getTitle(f)),['MyDiary','(Untitled)',]);鎴戜滑鍙互閫氳繃涓€涓暟缁勬潵缂栫爜鈥渏ust鈥濆拰鈥渘othing鈥濄€傛垜浠殑鏂规硶鐨勫ソ澶勫湪浜庡畠寰楀埌浜員ypeScript鐨勮壇濂芥敮鎸併€傜浉鍏抽摼鎺ュ師鏂囧湴鍧€锛歶ndefinedvs.null閲嶈鍘熺炕璇戣鍒?/p>
