棣栧厛瀵筳avascript鐨勭被鍨嬪啀鐔熸?zhèn)変竴閬?/strong>
javascript涓彉閲?variable)鐨勫?value)鏈夎繖鏍峰嚑縐嶇被鍨?type)錛?br />(ECMAscript Language Specification Edition 3 24-Mar-00)
8.1 The Undefined Type
The
Undefined type has exactly one value, called undefined. Any variable
that has not been assigned a value has the value undefined.
8.2 The Null Type
The Null type has exactly one value, called null.
8.3 The Boolean Type
The Boolean type represents a logical entity having two values, called true and false.
8.4 The String Type
The String type is the set of all finite ordered sequences of zero or more 16-bit unsigned integer values
(鈥渆lements鈥?.
8.5 The Number Type
The Number type has exactly 18437736874454810627 (that is, 264鈭?53+3) values, representing the doubleprecision
64-bit format IEEE 754 values as specified in the IEEE Standard for Binary Floating-Point Arithmetic,
except that the 9007199254740990 (that is, 253鈭?) distinct 鈥淣ot-a-Number鈥?values of the IEEE Standard are
represented in ECMAscript as a single special NaN value. (Note that the NaN value is produced by the program
expression NaN, assuming that the globally defined variable NaN has not been altered by program execution.)
8.6 The Object Type
An Object is an unordered collection of properties. Each property consists of a name, a value and a set of attributes.
鎴戜滑姣旇緝鍏蟲敞闈㈠悜瀵硅薄錛屾墍浠ュ鍏朵腑鐨凮bject綾誨瀷澶氬姞鐣欐剰銆?br />濡備笂闈㈢殑瀹氫箟錛孫bject綾誨瀷鏄棤搴忕殑灞炴х殑闆嗗悎銆傛瘡涓睘鎬?property)鏈夊悕縐幫紝鍊煎拰涓浜涙ц川(attributes)錛堝鍙錛屽彲鏋氫婦錛屼笉鍙垹錛屽唴閮ㄧ殑錛夈?br />
涓懼嚑涓緥瀛愶細
var a;//a鐜板湪瀵瑰簲涓涓鹼紝璇ュ肩殑綾誨瀷鏄?span style="FONT-WEIGHT: bold">Undefined
a = 1;//鐜板湪a瀵瑰簲涓涓狽umber綾誨瀷鐨勫?br />a = true;//鐜板湪a鐨勭被鍨嬪彉浜嗭紝鍙樻垚涓涓狟oolean綾誨瀷鐨勫箋?br />a = "x";//a鐜板湪瀵瑰簲涓涓猄tring綾誨瀷鐨勫?br />//錛堟敞鎰?x"鍜宯ew String("x")騫朵笉鐩稿悓錛?br />//璇村埌榪欓噷鎯沖埌javascript閲屼袱涓浉絳夋搷浣滅==鍜?==
//==鍙拡瀵瑰熀鏈殑鏁版嵁綾誨瀷錛屼笉瀵筄bject錛屽鏋滃緟姣旇緝鐨勪袱涓奸兘鏄疧bject鐨勮瘽
//榪斿洖false錛岄櫎闈炴槸鍚屼竴涓璞★紝濡傛灉鏈夋湁涓涓槸Object鐨勮瘽錛屽皢涔嬭漿鍖栦負鍜屽彟澶栦竴涓肩浉鍚岀被鍨嬬殑鍊?br />//鐒跺悗榪涜姣旇緝銆?==鍒欒姹備袱鑰呯被鍨嬩篃鐩稿悓銆?br />var b = new String("x");
alert(a == b);//true
alert(a===b);//false 鍥犱負綾誨瀷涓嶅悓
alert(typeof a);//string
alert(typeof b);//object
a = {};
//鏌ョ湅綾誨瀷鐨勬柟娉曟槸typeof錛屽彲浠ュ啓鎴恡ypeof a涔熷彲浠ュ啓鎴恡ypeof(a)
//鍙傜湅typeof鐨勮鏄?br />alert(typeof a);//object
alert(typeof true);//boolean
alert(typeof(typeof true))//string
typeof鐨勬墽琛岄昏緫
| Undefined | "undefined" |
| Null | "object" |
| Boolean | "boolean" |
| Number | "number" |
| String | "string" |
| Object (native and doesn鈥檛 implement [[Call]]) | "object" |
| Object (native and implements [[Call]]) | "function" |
| Object (host) | Implementation-dependent |
浠庝笂闈㈠彲浠ョ湅鍒板浜嶰bject綾誨瀷錛宼ypeof鏍規(guī)嵁鍊肩殑鎯呭喌榪斿洖object鎴杅unction銆?br />錛堟敞錛氭墍璋?/span>implement [[Call]]鎴戠殑鐞嗚В灝辨槸鎸囨槸鍚﹀彲浠ヤ綔涓哄嚱鏁拌皟鐢?span style="FONT-WEIGHT: bold" dragover="true">錛宯ative鏈変袱縐嶄竴縐嶆槸鍐呯疆鐨勫Array錛孌ate絳夊彟涓縐嶆槸鐢ㄦ埛鑷繁瀹氫箟鐨勩傞櫎姝や箣澶栧氨鏄痟ost鍗砵avascript鐨勫涓繪彁渚涚殑涓浜涘璞°傦級
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