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<html> <body> <script type="text/javascript"> var r, s = "this is a very very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong string", x = /^\s+|\s+$/g; document.writeln("字串測試"); (function(){ document.write("全域->全域："); var t = new Date(); for(var i = 0; i < 3000000; i++){ r = s; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("全域->本地："); var s = window.s; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = s; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("常量->本地："); var r; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = "this is a very very looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong string"; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("屬性->本地："); var r; var s = { 0: window.s }; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = s[0]; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("本地->本地："); var r; var s = window.s; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = s; } document.write(new Date() - t); document.writeln(""); })(); document.writeln("Regex測試"); (function(){ document.write("全域->全域："); var t = new Date(); for(var i = 0; i < 3000000; i++){ r = x; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("全域->本地："); var x = window.x; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = x; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("常量->本地："); var r; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = /^\s+|\s+$/g; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("屬性->本地："); var r; var x = { 0: window.x }; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = x[0]; } document.write(new Date() - t); document.writeln(""); })(); (function(){ document.write("本地->本地："); var r; var x = window.x; var t = new Date(); for(var i = 0; i < 3000000; i++){ r = x; } document.write(new Date() - t); document.writeln(""); })(); </script> </body> </html>
[Ctrl+A 全選 注:如需引入外部Js需重新整理才能執行]
注意：在IE中進行這個測試時需要先改變IE的"最大指令碼步數"：
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Styles]
"MaxScriptStatements"=dword:ffffffff
這麼看的話使用函數內的本地變數時效率要比用全域變數或者常量運算式高出許多。而屬性的效率就糟得很恐怖了，在Firefox和Safari中居然比利用全域變數還慢上好多倍。
直接用字串常量要比利用全域變數快，但建立Regex就比起用全域變數要慢上很多了。
觀察數字還可以發現：在Google Chrome、Opera和IE中，用屬性和利用全域變數相差不大（Opera的表現也許是其記憶體回收機製造成的），從這個現象上看的話，這三種瀏覽器中所謂的全域變數有可能根本就是全域對象的屬性。
