譛ｬ鬆√�逶ｮ谺｡ 逶ｮ谺｡ 谺｡鬆�: 11_Expressions 蜑埼��: 9_Type_Conversion
蛻ｶ蠕｡縺� ECMAScript 縺ｮ螳溯｡悟庄閭ｽ繧ｳ繝ｼ繝峨↓霆｢騾√＆繧後ｋ譎ゅ↓縲∝宛蠕｡縺ｯ 螳溯｡後さ繝ｳ繝�く繧ｹ繝� 縺ｫ蜈･繧九ゅい繧ｯ繝�ぅ繝悶↑螳溯｡後さ繝ｳ繝�く繧ｹ繝医�隲也炊逧�↓繧ｹ繧ｿ繝�け繧貞ｽ｢謌舌☆繧九ゅ％縺ｮ隲也炊逧�せ繧ｿ繝�け荳翫�螳溯｡後さ繝ｳ繝�く繧ｹ繝医�鬆らせ縺後∝ｮ溯｡後＆繧後ｋ螳溯｡後さ繝ｳ繝�く繧ｹ繝医〒縺ゅｋ縲�
Function 繧ｪ繝悶ず繧ｧ繧ｯ繝医↓縺ｯ 2 遞ｮ鬘槭≠繧�:
Function 繧ｪ繝悶ず繧ｧ繧ｯ繝医ｒ菴ｿ逕ｨ縺励※蜍慕噪縺ｫ逕滓�縺輔ｌ繧九�parseInt 繧� Math.exp 縺ｮ繧医≧縺ｪ縲∬ｨ隱槭�邨�ｾｼ縺ｿ繧ｪ繝悶ず繧ｧ繧ｯ繝医〒縺ゅｋ縲ょｮ溯｣��縲∵悽莉墓ｧ倥↓險倩ｿｰ縺輔ｌ縺ｪ縺�ｮ溯｣�ｾ晏ｭ倥�蜀�Κ髢｢謨ｰ繧呈署萓帙＠縺ｦ繧ゅｈ縺�ゅ％繧後ｉ縺ｮ髢｢謨ｰ縺ｯ ECMAScript 譁�ｳ輔↓險倩ｿｰ縺輔ｌ繧句ｮ溯｡悟庄閭ｽ繧ｳ繝ｼ繝峨ｒ蜷ｫ縺ｾ縺ｪ縺�ょｾ薙▲縺ｦ縺昴ｌ繧峨�螳溯｡後さ繝ｳ繝�く繧ｹ繝医�縺薙�隴ｰ隲悶°繧蛾勁螟悶＆繧後ｋ縲�ECMAScript 縺ｮ螳溯｡悟庄閭ｽ繧ｳ繝ｼ繝峨�遞ｮ鬘槭� 3 縺､縺ゅｋ:
蜷�ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医� 螟画焚繧ｪ繝悶ず繧ｧ繧ｯ繝� (variable object) 縺ｫ邨舌�莉倥￠繧峨ｌ縺ｦ縺�ｋ縲ゅた繝ｼ繧ｹ繝�く繧ｹ繝亥�縺ｫ螳｣險縺輔ｌ縺溷､画焚縺ｨ髢｢謨ｰ縺ｯ螟画焚繧ｪ繝悶ず繧ｧ繧ｯ繝医�繝励Ο繝代ユ繧｣縺ｫ霑ｽ蜉�縺輔ｌ繧九る未謨ｰ繧ｳ繝ｼ繝峨↓縺､縺�※縺ｯ縲√ヱ繝ｩ繝｡繝ｼ繧ｿ縺悟､画焚繧ｪ繝悶ず繧ｧ繧ｯ繝医�繝励Ο繝代ユ繧｣縺ｫ霑ｽ蜉�縺輔ｌ繧九�
縺ｩ縺ｮ繧ｪ繝悶ず繧ｧ繧ｯ繝医′螟画焚繧ｪ繝悶ず繧ｧ繧ｯ繝医↓菴ｿ繧上ｌ繧九°縲√←縺ｮ螻樊ｧ縺後�繝ｭ繝代ユ繧｣縺ｫ菴ｿ繧上ｌ繧九°縺ｯ縲√さ繝ｼ繝峨�蝙九↓萓晏ｭ倥☆繧九ゅ＠縺九＠縲∝ｾ後�謖ｯ繧玖�縺��邱乗峡逧�〒縺ゅｋ縲ょｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧九→縲√�繝ｭ繝代ユ繧｣縺ｯ谺｡縺ｮ鬆�↓螟画焚繧ｪ繝悶ず繧ｧ繧ｯ繝医↓邨舌�莉倥￠繧峨ｌ繧�:
蜷�ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医� 繧ｹ繧ｳ繝ｼ繝鈴｣骼� (scope chain) 縺ｫ髢｢騾｣莉倥￠繧峨ｌ縺ｦ縺�ｋ縲ゅせ繧ｳ繝ｼ繝鈴｣骼悶�繧ｪ繝悶ず繧ｧ繧ｯ繝医�繝ｪ繧ｹ繝医〒縲！dentifier 縺ｮ隧穂ｾ｡縺ｮ髫帙↓讀懃ｴ｢縺輔ｌ繧九ょ宛蠕｡縺悟ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧九→縺阪√さ繝ｼ繝牙梛豈弱↓繧ｪ繝悶ず繧ｧ繧ｯ繝磯寔蜷医�蛻晄悄蛟､繧剃ｼｴ縺�せ繧ｳ繝ｼ繝鈴｣骼悶′逕滓�縺輔ｌ縲∫ｵ�∩霎ｼ縺ｾ繧後ｋ縲ょｮ溯｡後さ繝ｳ繝�く繧ｹ繝亥�縺ｫ縺翫￠繧句ｮ溯｡後�髢薙∝ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医�繧ｹ繧ｳ繝ｼ繝鈴｣骼悶� with 譁�(12.10) 縺ｨ catch 繧ｯ繝ｭ繝ｼ繧ｺ(12.14) 縺ｫ繧医▲縺ｦ縺ｮ縺ｿ蠖ｱ髻ｿ繧貞所縺ｼ縺輔ｌ繧九�
螳溯｡御ｸｭ縲∵ｧ区枚逧�函謌占ｦ丞援 PrimaryExpression : Identifier 縺ｯ谺｡縺ｮ繧｢繝ｫ繧ｴ繝ｪ繧ｺ繝�縺ｧ隧穂ｾ｡縺輔ｌ繧�:
隴伜挨蟄占ｩ穂ｾ｡縺ｮ邨先棡縺ｯ蟶ｸ縺ｫ縲∬ｭ伜挨蟄先枚蟄怜�縺ｨ遲峨＠縺�Γ繝ｳ繝仙錐謌仙�繧呈戟縺､ Reference 蝙九�蛟､縺ｧ縺ゅｋ縲�
蛻ｶ蠕｡縺御ｻｻ諢上�螳溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧句燕縺ｫ逕滓�縺輔ｌ繧九∽ｸ諢冗噪縺ｪ 繧ｰ繝ｭ繝ｼ繝舌Ν繧ｪ繝悶ず繧ｧ繧ｯ繝� (繧ｻ繧ｯ繧ｷ繝ｧ繝ｳ15.1) 縺悟ｭ伜惠縺吶ｋ縲よ怙蛻昴�繧ｰ繝ｭ繝ｼ繝舌Ν繧ｪ繝悶ず繧ｧ繧ｯ繝医�谺｡縺ｮ繝励Ο繝代ユ繧｣繧呈戟縺､:
蛻ｶ蠕｡縺悟ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧翫・CMAScript 繧ｳ繝ｼ繝峨′螳溯｡後＆繧後ｌ縺ｰ縲√げ繝ｭ繝ｼ繝舌Ν繧ｪ繝悶ず繧ｧ繧ｯ繝医↓霑ｽ蜉�繝励Ο繝代ユ繧｣繧定ｿｽ蜉�縺励※繧ゅ∝�譛溘�繝励Ο繝代ユ繧｣繧貞､画峩縺励※繧ゅｈ縺��
髢｢謨ｰ繧ｳ繝ｼ繝峨↓繧医▲縺ｦ蛻ｶ蠕｡縺悟ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧九→縺阪� Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医→蜻ｼ縺ｰ繧後ｋ繧ｪ繝悶ず繧ｧ繧ｯ繝医′逕滓�縺輔ｌ螳溯｡後さ繝ｳ繝�く繧ｹ繝医↓邨舌�莉倥￠繧峨ｌ繧九� Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医�螻樊ｧ { DontDelete } 縺ｮ繝励Ο繝代ユ繧｣ arguments 縺ｧ蛻晄悄蛹悶＆繧後ｋ縲ゅ％縺ｮ繝励Ο繝代ユ繧｣縺ｮ蛻晄悄蛟､縺ｯ荳九↓霑ｰ縺ｹ繧� arguments 繧ｪ繝悶ず繧ｧ繧ｯ繝医〒縺ゅｋ縲�
Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医�螟画焚縺ｮ螳滉ｽ灘喧繧堤岼逧�→縺励◆螟画焚繧ｪ繝悶ず繧ｧ繧ｯ繝医→縺励※菴ｿ逕ｨ縺輔ｌ繧九�
Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医�邏皮ｲ九↓莉墓ｧ倥�繝｡繧ｫ繝九ぜ繝�縺ｧ縺ゅｋ縲� Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医∈縺ｮ繧｢繧ｯ繧ｻ繧ｹ縺ｯ ECMAScript 繝励Ο繧ｰ繝ｩ繝�縺ｫ縺ｯ荳榊庄閭ｽ縺ｧ縺ゅｋ縲� Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医�繝｡繝ｳ繝舌∈縺ｮ繧｢繧ｯ繧ｻ繧ｹ縺ｯ蜿ｯ閭ｽ縺�縺後� Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝郁�霄ｫ縺ｸ縺ｮ繧｢繧ｯ繧ｻ繧ｹ縺ｯ縺ｧ縺阪↑縺�ょ渕貅悶が繝悶ず繧ｧ繧ｯ繝医′ Activation 繧ｪ繝悶ず繧ｧ繧ｯ繝医〒縺ゅｋ Reference 蛟､縺ｫ蜻ｼ蜃ｺ謫堺ｽ懊′驕ｩ逕ｨ縺輔ｌ繧九→縺阪√◎縺ｮ蜻ｼ蜃ｺ縺ｮ this 蛟､縺ｨ縺励※ null 縺御ｽｿ繧上ｌ繧九�
繧｢繧ｯ繝�ぅ繝悶↑螳溯｡後さ繝ｳ繝�く繧ｹ繝医◎繧後◇繧後↓邨舌�莉倥￠繧峨ｌ繧� this 蛟､縺後≠繧九�this 蛟､縺ｯ蜻ｼ蜃ｺ蛛ｴ縺ｨ螳溯｡後＆繧後ｋ繧ｳ繝ｼ繝牙梛縺ｫ萓晏ｭ倥＠縲∝宛蠕｡縺悟ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧九→縺阪↓豎ｺ螳壹＆繧後ｋ縲ょｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓邨舌�莉倥￠繧峨ｌ繧� this 蛟､縺ｯ荳榊､峨〒縺ゅｋ縲�
髢｢謨ｰ繧ｳ繝ｼ繝峨↓繧医▲縺ｦ蛻ｶ蠕｡縺悟ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医↓蜈･繧九→縺阪� arguments 繧ｪ繝悶ず繧ｧ繧ｯ繝医′菴懈�縺輔ｌ谺｡縺ｮ繧医≧縺ｫ蛻晄悄蛹悶＆繧後ｋ:
蜷�未謨ｰ縺ｨ繧ｳ繝ｳ繧ｹ繝医Λ繧ｯ繧ｿ縺ｮ蜻ｼ蜃ｺ縺ｯ縲∵眠縺励＞螳溯｡後さ繝ｳ繝�く繧ｹ繝医ｒ髢句ｧ九☆繧九る未謨ｰ縺後◎繧瑚�霄ｫ縺ｮ蜀榊ｸｰ逧�他蜃ｺ縺ｧ縺ゅ▲縺ｦ繧ゅ∝推繝ｪ繧ｿ繝ｼ繝ｳ縺ｯ螳溯｡後さ繝ｳ繝�く繧ｹ繝医ｒ邨ゆｺ�☆繧九よ兜縺偵ｉ繧後◆萓句､悶′蜿励￠蜿悶ｉ繧後↑縺��ｴ蜷医�縲∽ｸ縺､莉･荳翫�螳溯｡後さ繝ｳ繝�く繧ｹ繝医ｒ邨ゆｺ�＠縺ｦ繧医＞縲�
蛻ｶ蠕｡縺悟ｮ溯｡後さ繝ｳ繝�く繧ｹ繝医ｒ髢句ｧ九☆繧九→縺阪√せ繧ｳ繝ｼ繝鈴｣骼悶′逕滓�繝ｻ蛻晄悄蛹悶＆繧後∝､画焚縺ｮ螳滉ｽ灘喧縺瑚｡後ｏ繧後》his 蛟､縺梧ｱｺ螳壹＆繧後ｋ縲�
繧ｹ繧ｳ繝ｼ繝鈴｣骼悶�螳滉ｽ灘喧縲∝､画焚縺ｮ螳滉ｽ灘喧縲》his 蛟､縺ｮ豎ｺ螳壹�縲�幕蟋九☆繧九さ繝ｼ繝牙梛縺ｫ萓晏ｭ倥☆繧九�
this 蛟､縺ｯ繧ｰ繝ｭ繝ｼ繝舌Ν繧ｪ繝悶ず繧ｧ繧ｯ繝医〒縺ゅｋ縲�蛻ｶ蠕｡縺� eval 繧ｳ繝ｼ繝峨�螳溯｡後さ繝ｳ繝�く繧ｹ繝医ｒ髢句ｧ九☆繧九→縺阪∝燕縺ｮ繧｢繧ｯ繝�ぅ繝悶↑螳溯｡後さ繝ｳ繝�く繧ｹ繝医�縲� 蜻ｼ蜃ｺ繧ｳ繝ｳ繝�く繧ｹ繝� 縺ｨ縺励※蜿ら�縺輔ｌ縲√せ繧ｳ繝ｼ繝鈴｣骼悶∝､画焚繧ｪ繝悶ず繧ｧ繧ｯ繝医� this 蛟､縺ｮ豎ｺ螳壹↓菴ｿ逕ｨ縺輔ｌ繧九ょ他蜃ｺ繧ｳ繝ｳ繝�く繧ｹ繝医′縺ｪ縺代ｌ縺ｰ縲√せ繧ｳ繝ｼ繝鈴｣骼悶∝､画焚縺ｮ螳滉ｽ灘喧縲》his 蛟､縺ｮ豎ｺ螳壹�蛻晄悄蛹悶�縲√げ繝ｭ繝ｼ繝舌Ν繧ｳ繝ｼ繝峨→縺励※陦後ｏ繧後ｋ縲�
with 螳｣險縺翫ｈ縺ｳ catch 繧ｯ繝ｭ繝ｼ繧ｺ縺ｫ繧医▲縺ｦ蜻ｼ蜃ｺ繧ｳ繝ｳ繝�く繧ｹ繝医�繧ｹ繧ｳ繝ｼ繝鈴｣骼悶↓霑ｽ蜉�縺輔ｌ繧九が繝悶ず繧ｧ繧ｯ繝医ｒ蜷ｫ繧縲�this 蛟､縺ｯ蜻ｼ蜃ｺ繧ｳ繝ｳ繝�く繧ｹ繝医� this 蛟､縺ｨ蜷後§縺ｧ縺ゅｋ縲�this 蛟､縺ｯ蜻ｼ蜃ｺ蛛ｴ縺梧署萓帙☆繧九ょ他蜃ｺ蛛ｴ縺梧署萓帙☆繧� this 蛟､縺後が繝悶ず繧ｧ繧ｯ繝医〒縺ｪ縺��ｴ蜷�(null 縺ｧ縺ゅｋ蝣ｴ蜷医ｒ蜷ｫ繧)縲� this 蛟､縺ｯ繧ｰ繝ｭ繝ｼ繝舌Ν繧ｪ繝悶ず繧ｧ繧ｯ繝医→縺吶ｋ縲�