{"id":583,"date":"2017-02-22T16:07:58","date_gmt":"2017-02-22T08:07:58","guid":{"rendered":"http:\/\/blog.feizhaojun.com\/?p=583"},"modified":"2017-02-22T16:15:15","modified_gmt":"2017-02-22T08:15:15","slug":"%e5%a3%b0%e6%98%8e%e5%bc%8f%e7%bc%96%e7%a8%8b%e5%92%8c%e5%91%bd%e4%bb%a4%e5%bc%8f%e7%bc%96%e7%a8%8b%e7%9a%84%e6%af%94%e8%be%83","status":"publish","type":"post","link":"https:\/\/feizhaojun.com\/?p=583","title":{"rendered":"\u58f0\u660e\u5f0f\u7f16\u7a0b\u548c\u547d\u4ee4\u5f0f\u7f16\u7a0b\u7684\u6bd4\u8f83"},"content":{"rendered":"<p>\u539f\u6587\uff1a<a href=\"http:\/\/latentflip.com\/imperative-vs-declarative\">http:\/\/latentflip.com\/imperative-vs-declarative<\/a><\/p>\n<p>\u5148\u7edf\u4e00\u4e00\u4e0b\u6982\u5ff5\uff0c\u6211\u4eec\u6709\u4e24\u79cd\u7f16\u7a0b\u65b9\u5f0f\uff1a\u547d\u4ee4\u5f0f\u548c\u58f0\u660e\u5f0f\u3002<\/p>\n<p>\u6211\u4eec\u53ef\u4ee5\u50cf\u4e0b\u9762\u8fd9\u6837\u5b9a\u4e49\u5b83\u4eec\u4e4b\u95f4\u7684\u4e0d\u540c\uff1a<\/p>\n<p>\u547d\u4ee4\u5f0f\u7f16\u7a0b\uff1a\u547d\u4ee4\u201c\u673a\u5668\u201d\u5982\u4f55\u53bb\u505a\u4e8b\u60c5(how)\uff0c\u8fd9\u6837\u4e0d\u7ba1\u4f60\u60f3\u8981\u7684\u662f\u4ec0\u4e48(what)\uff0c\u5b83\u90fd\u4f1a\u6309\u7167\u4f60\u7684\u547d\u4ee4\u5b9e\u73b0\u3002<br \/>\n\u58f0\u660e\u5f0f\u7f16\u7a0b\uff1a\u544a\u8bc9\u201c\u673a\u5668\u201d\u4f60\u60f3\u8981\u7684\u662f\u4ec0\u4e48(what)\uff0c\u8ba9\u673a\u5668\u60f3\u51fa\u5982\u4f55\u53bb\u505a(how)\u3002<\/p>\n<p><strong>\u58f0\u660e\u5f0f\u7f16\u7a0b\u548c\u547d\u4ee4\u5f0f\u7f16\u7a0b\u7684\u4ee3\u7801\u4f8b\u5b50<\/strong><\/p>\n<p>\u4e3e\u4e2a\u7b80\u5355\u7684\u4f8b\u5b50\uff0c\u5047\u8bbe\u6211\u4eec\u60f3\u8ba9\u4e00\u4e2a\u6570\u7ec4\u91cc\u7684\u6570\u503c\u7ffb\u500d\u3002<\/p>\n<p>\u6211\u4eec\u7528\u547d\u4ee4\u5f0f\u7f16\u7a0b\u98ce\u683c\u5b9e\u73b0\uff0c\u50cf\u4e0b\u9762\u8fd9\u6837\uff1a<\/p>\n<p>[javascript]<br \/>\nvar numbers = [1,2,3,4,5]<br \/>\nvar doubled = []<br \/>\nfor(var i = 0; i &lt; numbers.length; i++) {<br \/>\n  var newNumber = numbers[i] * 2<br \/>\n  doubled.push (newNumber)<br \/>\n}<br \/>\nconsole.log (doubled) \/\/=&gt; [2,4,6,8,10]<br \/>\n[\/javascript]<\/p>\n<p>\u6211\u4eec\u76f4\u63a5\u904d\u5386\u6574\u4e2a\u6570\u7ec4\uff0c\u53d6\u51fa\u6bcf\u4e2a\u5143\u7d20\uff0c\u4e58\u4ee5\u4e8c\uff0c\u7136\u540e\u628a\u7ffb\u500d\u540e\u7684\u503c\u653e\u5165\u65b0\u6570\u7ec4\uff0c\u6bcf\u6b21\u90fd\u8981\u64cd\u4f5c\u8fd9\u4e2a<strong>doubled<\/strong>\u6570\u7ec4\uff0c\u76f4\u5230\u8ba1\u7b97\u5b8c\u6240\u6709\u5143\u7d20\u3002<br \/>\n\u800c\u4f7f\u7528\u58f0\u660e\u5f0f\u7f16\u7a0b\u65b9\u6cd5\uff0c\u6211\u4eec\u53ef\u4ee5\u7528 <strong>Array.map<\/strong> \u51fd\u6570\uff0c\u50cf\u4e0b\u9762\u8fd9\u6837\uff1a<\/p>\n<p>[javascript]<br \/>\nvar numbers = [1,2,3,4,5]<br \/>\nvar doubled = numbers.map (function (n) {<br \/>\n  return n * 2<br \/>\n})<br \/>\nconsole.log (doubled) \/\/=&gt; [2,4,6,8,10]<br \/>\n[\/javascript]<\/p>\n<p><strong>map<\/strong>\u5229\u7528\u5f53\u524d\u7684\u6570\u7ec4\u521b\u5efa\u4e86\u4e00\u4e2a\u65b0\u6570\u7ec4\uff0c\u65b0\u6570\u7ec4\u91cc\u7684\u6bcf\u4e2a\u5143\u7d20\u90fd\u662f\u7ecf\u8fc7\u4e86\u4f20\u5165<strong>map(function (n) { return n*2 })<\/strong>\u7684\u5904\u7406\u3002<\/p>\n<p><strong>map<\/strong>\u51fd\u6570\u6240\u505a\u7684\u4e8b\u60c5\u662f\u5c06\u76f4\u63a5\u904d\u5386\u6574\u4e2a\u6570\u7ec4\u7684\u8fc7\u7a0b\u5f52\u7eb3\u62bd\u79bb\u51fa\u6765\uff0c\u8ba9\u6211\u4eec\u4e13\u6ce8\u4e8e\u63cf\u8ff0\u6211\u4eec\u60f3\u8981\u7684\u662f\u4ec0\u4e48(what)\u3002\u6ce8\u610f\uff0c\u6211\u4eec\u4f20\u5165map\u7684\u662f\u4e00\u4e2a\u7eaf\u51fd\u6570\uff1b\u5b83\u4e0d\u5177\u6709\u4efb\u4f55\u526f\u4f5c\u7528(\u4e0d\u4f1a\u6539\u53d8\u5916\u90e8\u72b6\u6001)\uff0c\u5b83\u53ea\u662f\u63a5\u6536\u4e00\u4e2a\u6570\u5b57\uff0c\u8fd4\u56de\u4e58\u4ee5\u4e8c\u540e\u7684\u503c\u3002<\/p>\n<p>\u5728\u4e00\u4e9b\u5177\u6709\u51fd\u6570\u5f0f\u7f16\u7a0b\u7279\u5f81\u7684\u8bed\u8a00\u91cc\uff0c\u5bf9\u4e8e list \u6570\u636e\u7c7b\u578b\u7684\u64cd\u4f5c\uff0c\u8fd8\u6709\u4e00\u4e9b\u5176\u4ed6\u5e38\u7528\u7684\u58f0\u660e\u5f0f\u7684\u51fd\u6570\u65b9\u6cd5\u3002\u4f8b\u5982\uff0c\u6c42\u4e00\u4e2alist\u91cc\u6240\u6709\u503c\u7684\u548c\uff0c\u547d\u4ee4\u5f0f\u7f16\u7a0b\u4f1a\u8fd9\u6837\u505a\uff1a<\/p>\n<p>[javascript]<br \/>\nvar numbers = [1,2,3,4,5]<br \/>\nvar total = 0 for(var i = 0; i &lt; numbers.length; i++) {<br \/>\n  total += numbers[i]<br \/>\n}<br \/>\nconsole.log (total) \/\/=&gt; 15<br \/>\n[\/javascript]<\/p>\n<p>\u800c\u5728\u58f0\u660e\u5f0f\u7f16\u7a0b\u65b9\u5f0f\u91cc\uff0c\u6211\u4eec\u4f7f\u7528<strong>reduce<\/strong>\u51fd\u6570\uff1a<\/p>\n<p>[javascript]<br \/>\nvar numbers = [1,2,3,4,5]<br \/>\nvar total = numbers.reduce (function (sum, n) {<br \/>\n  return sum + n<br \/>\n});<br \/>\nconsole.log (total) \/\/=&gt; 15<br \/>\n[\/javascript]<\/p>\n<p><strong>reduce<\/strong>\u51fd\u6570\u5229\u7528\u4f20\u5165\u7684\u51fd\u6570\u628a\u4e00\u4e2alist\u8fd0\u7b97\u6210\u4e00\u4e2a\u503c\u3002\u5b83\u4ee5\u8fd9\u4e2a\u51fd\u6570\u4e3a\u53c2\u6570\uff0c\u6570\u7ec4\u91cc\u7684\u6bcf\u4e2a\u5143\u7d20\u90fd\u8981\u7ecf\u8fc7\u5b83\u7684\u5904\u7406\u3002\u6bcf\u4e00\u6b21\u8c03\u7528\uff0c\u7b2c\u4e00\u4e2a\u53c2\u6570(\u8fd9\u91cc\u662f<strong>sum<\/strong>)\u90fd\u662f\u8fd9\u4e2a\u51fd\u6570\u5904\u7406\u524d\u4e00\u4e2a\u503c\u65f6\u8fd4\u56de\u7684\u7ed3\u679c\uff0c\u800c\u7b2c\u4e8c\u4e2a\u53c2\u6570(<strong>n<\/strong>)\u5c31\u662f\u5f53\u524d\u5143\u7d20\u3002\u8fd9\u6837\u4e0b\u6765\uff0c\u6bcf\u6b64\u5904\u7406\u7684\u65b0\u5143\u7d20\u90fd\u4f1a\u5408\u8ba1\u5230sum\u4e2d\uff0c\u6700\u7ec8\u6211\u4eec\u5f97\u5230\u7684\u662f\u6574\u4e2a\u6570\u7ec4\u7684\u548c\u3002<\/p>\n<p>\u540c\u6837\uff0c<strong>reduce<\/strong>\u51fd\u6570\u5f52\u7eb3\u62bd\u79bb\u4e86\u6211\u4eec\u5982\u4f55\u904d\u5386\u6570\u7ec4\u548c\u72b6\u6001\u7ba1\u7406\u90e8\u5206\u7684\u5b9e\u73b0\uff0c\u63d0\u4f9b\u7ed9\u6211\u4eec\u4e00\u4e2a\u901a\u7528\u7684\u65b9\u5f0f\u6765\u628a\u4e00\u4e2alist\u5408\u5e76\u6210\u4e00\u4e2a\u503c\u3002\u6211\u4eec\u9700\u8981\u505a\u7684\u53ea\u662f\u6307\u660e\u6211\u4eec\u60f3\u8981\u7684\u662f\u4ec0\u4e48\uff1f<\/p>\n<p><strong>\u58f0\u660e\u5f0f\u7f16\u7a0b\u5f88\u5947\u602a\u5417\uff1f<\/strong><\/p>\n<p>\u5982\u679c\u4f60\u4e4b\u524d\u6ca1\u6709\u542c\u8bf4\u8fc7map\u548creduce\u51fd\u6570\uff0c\u4f60\u7684\u7b2c\u4e00\u611f\u89c9\uff0c\u6211\u76f8\u4fe1\uff0c\u5c31\u4f1a\u662f\u8fd9\u6837\u3002\u4f5c\u4e3a\u7a0b\u5e8f\u5458\uff0c\u6211\u4eec\u975e\u5e38\u4e60\u60ef\u53bb\u6307\u51fa\u4e8b\u60c5\u5e94\u8be5\u5982\u4f55\u8fd0\u884c\u3002\u201c\u53bb\u904d\u5386\u8fd9\u4e2alist\u201d\uff0c\u201cif \u8fd9\u79cd\u60c5\u51b5 then \u90a3\u6837\u505a\u201d\uff0c\u201c\u628a\u8fd9\u4e2a\u65b0\u503c\u8d4b\u7ed9\u8fd9\u4e2a\u53d8\u91cf\u201d\u3002\u5f53\u6211\u4eec\u5df2\u7ecf\u77e5\u9053\u4e86\u5982\u4f55\u544a\u8bc9\u673a\u5668\u8be5\u5982\u4f55\u505a\u4e8b\u65f6\uff0c\u4e3a\u4ec0\u4e48\u6211\u4eec\u9700\u8981\u53bb\u5b66\u4e60\u8fd9\u79cd\u770b\u8d77\u6765\u6709\u4e9b\u602a\u5f02\u7684\u5f52\u7eb3\u62bd\u79bb\u51fa\u6765\u7684\u51fd\u6570\u5de5\u5177\uff1f<\/p>\n<p>\u5728\u5f88\u591a\u60c5\u51b5\u4e2d\uff0c\u547d\u4ee4\u5f0f\u7f16\u7a0b\u5f88\u597d\u7528\u3002\u5f53\u6211\u4eec\u5199\u4e1a\u52a1\u903b\u8f91\uff0c\u6211\u4eec\u901a\u5e38\u5fc5\u987b\u8981\u5199\u547d\u4ee4\u5f0f\u4ee3\u7801\uff0c\u6ca1\u6709\u53ef\u80fd\u5728\u6211\u4eec\u7684\u4e13\u9879\u4e1a\u52a1\u91cc\u4e5f\u5b58\u5728\u4e00\u4e2a\u53ef\u4ee5\u5f52\u7eb3\u62bd\u79bb\u7684\u5b9e\u73b0\u3002<\/p>\n<p>\u4f46\u662f\uff0c\u5982\u679c\u6211\u4eec\u82b1\u65f6\u95f4\u53bb\u5b66\u4e60(\u6216\u53d1\u73b0)\u58f0\u660e\u5f0f\u7684\u53ef\u4ee5\u5f52\u7eb3\u62bd\u79bb\u7684\u90e8\u5206\uff0c\u5b83\u4eec\u80fd\u4e3a\u6211\u4eec\u7684\u7f16\u7a0b\u5e26\u6765\u5de8\u5927\u7684\u4fbf\u6377\u3002\u9996\u5148\uff0c\u6211\u53ef\u4ee5\u5c11\u5199\u4ee3\u7801\uff0c\u8fd9\u5c31\u662f\u901a\u5f80\u6210\u529f\u7684\u6377\u5f84\u3002\u800c\u4e14\u5b83\u4eec\u80fd\u8ba9\u6211\u4eec\u7ad9\u5728\u66f4\u9ad8\u7684\u5c42\u9762\u662f\u601d\u8003\uff0c\u7ad9\u5728\u4e91\u7aef\u601d\u8003\u6211\u4eec\u60f3\u8981\u7684\u662f\u4ec0\u4e48\uff0c\u800c\u4e0d\u662f\u7ad9\u5728\u6ce5\u91cc\u601d\u8003\u4e8b\u60c5\u8be5\u5982\u4f55\u53bb\u505a\u3002<\/p>\n<p><strong>\u58f0\u660e\u5f0f\u7f16\u7a0b\u8bed\u8a00\uff1aSQL<\/strong><\/p>\n<p>\u4e5f\u8bb8\u4f60\u8fd8\u4e0d\u80fd\u660e\u767d\uff0c\u4f46\u6709\u4e00\u4e2a\u5730\u65b9\uff0c\u4f60\u4e5f\u8bb8\u5df2\u7ecf\u7528\u5230\u4e86\u58f0\u660e\u5f0f\u7f16\u7a0b\uff0c\u90a3\u5c31\u662fSQL\u3002<\/p>\n<p>\u4f60\u53ef\u4ee5\u628a SQL \u5f53\u505a\u4e00\u4e2a\u5904\u7406\u6570\u636e\u7684\u58f0\u660e\u5f0f\u67e5\u8be2\u8bed\u8a00\u3002\u5b8c\u5168\u7528SQL\u5199\u4e00\u4e2a\u5e94\u7528\u7a0b\u5e8f\uff1f\u8fd9\u4e0d\u53ef\u80fd\u3002\u4f46\u5982\u679c\u662f\u5904\u7406\u76f8\u4e92\u5173\u8054\u7684\u6570\u636e\u96c6\uff0c\u5b83\u5c31\u663e\u7684\u65e0\u6bd4\u5f3a\u5927\u4e86\u3002<\/p>\n<p>\u50cf\u4e0b\u9762\u8fd9\u6837\u7684\u67e5\u8be2\u8bed\u53e5\uff1a<\/p>\n<p>[javascript]<br \/>\nSELECT * from dogs<br \/>\nINNER JOIN owners<br \/>\nWHERE dogs.owner_id = owners.id<br \/>\n[\/javascript]<\/p>\n<p>\u5982\u679c\u6211\u4eec\u7528\u547d\u4ee4\u5f0f\u7f16\u7a0b\u65b9\u5f0f\u5b9e\u73b0\u8fd9\u6bb5\u903b\u8f91\uff1a<\/p>\n<p>[javascript]<br \/>\n\/\/dogs = [{name: 'Fido', owner_id: 1}, {...}, ... ]<br \/>\n\/\/owners = [{id: 1, name: 'Bob'}, {...}, ...] var dogsWithOwners = []<br \/>\nvar dog, owner<br \/>\nfor(var di=0; di &lt; dogs.length; di++) {<br \/>\n  dog = dogs[di]<br \/>\n  for(var oi=0; oi &lt; owners.length; oi++) {<br \/>\n    owner = owners[oi]<br \/>\n    if (owner &amp;&amp; dog.owner_id == owner.id) {<br \/>\n      dogsWithOwners.push ({<br \/>\n        dog: dog,<br \/>\n        owner: owner<br \/>\n      })<br \/>\n    }<br \/>\n  }}<br \/>\n}<br 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