{"id":1137,"date":"2012-03-21T22:43:11","date_gmt":"2012-03-21T14:43:11","guid":{"rendered":"http:\/\/leegorous.net\/blog\/?p=1137"},"modified":"2012-03-21T22:48:43","modified_gmt":"2012-03-21T14:48:43","slug":"js-number-precision","status":"publish","type":"post","link":"http:\/\/leegorous.net\/blog\/2012\/03\/21\/js-number-precision\/","title":{"rendered":"Number \u7684\u5931\u771f\u8fb9\u754c"},"content":{"rendered":"<p>Javascript \u4e2d\u7684 Number \u662f\u4e2a\u795e\u5947\u7684\u7c7b\u578b\uff0c\u5b83\u6a21\u7cca\u4e86 <strong>\u6574\u5f62<\/strong> \u548c <strong>\u6d6e\u70b9\u6570<\/strong> \u4e4b\u95f4\u7684\u8fb9\u754c\uff0c\u5f53\u4f60\u62ff\u5230\u4e00\u4e2a Number \u7684\u65f6\u5019\uff0c\u5b83\u5c31\u53ea\u662f\u4e00\u4e2a <a href=\"https:\/\/developer.mozilla.org\/en\/JavaScript\/Reference\/Global_Objects\/Number\" target=\"_blank\">Number<\/a>\uff0c\u800c\u4e14\u53ef\u4ee5\u5f88\u65b9\u4fbf\u5730\u8868\u793a\u975e\u5e38\u5927\u7684\u6570 Number.MAX_VALUE \u6216\u8005\uff0c\u6216\u8005\u975e\u5e38\u5c0f\u7684\u6570 Number.MIN_VALUE\u3002<br \/>\n\u5b9e\u9645\u5e94\u7528\u573a\u5408\u91cc\u9762\u9664\u4e86\u8981\u8868\u793a\u5927\u6570\u548c\u5c0f\u6570\uff0c\u6709\u65f6\u8fd8\u4f1a\u8bb2\u7a76\u4e0b\u7cbe\u5ea6\u7684\u3002<\/p>\n<p>\u5728 <a href=\"https:\/\/developer.mozilla.org\/en\/JavaScript\/Reference\/Global_Objects\/Number\/toPrecision\">MDN \u7684 Number.toPrecision<\/a> \u4e2d\u6709\u63cf\u8ff0 <em>\u201c<a href=\"https:\/\/developer.mozilla.org\/en\/ECMAScript\" target=\"_blank\">ECMA-262<\/a> only requires a precision of up to 21 significant digits. Other implementations may not support precisions higher than required by the standard.\u201d<\/em><\/p>\n<p>\u6211\u4eec\u53ef\u4ee5\u77e5\u9053 JavaScript \u7684\u7cbe\u5ea6\u5728 21 \u4f4d\u3002\u7a76\u7adf\u662f\u4e0d\u662f\u4ee3\u8868\u53ea\u8981\u5c11\u4e8e 21 \u4f4d\u7684\u6570\u90fd\u80fd\u7cbe\u786e\u8868\u793a\u5462\uff1f\u7b80\u5355\u6765\u4e2a\u8bd5\u9a8c\u5c31\u53ef\u4ee5\u77e5\u9053\u4e86\u3002\u53ef\u4ee5\u731b\u51fb<a href=\"http:\/\/leegorous.net\/tools\/number.html\" target=\"_blank\">\u8fd9\u4e2a\u94fe\u63a5 \u770b\u770b\u4f60\u7684\u6d4f\u89c8\u5668\u91cc\u7684 js \u5230\u5e95\u80fd\u6709\u591a\u7cbe\u786e<\/a>\u3002<\/p>\n<pre class=\"brush: js\">\r\nvar arr = [];\r\nfor(var i = 0; i&lt; 21; i++) {\r\n  arr.push(&#039;9&#039;);\r\n  console.log((i+1) + &#039; : &#039; + arr.join(&#039;&#039;) + &#039; &gt;&gt;&#039; + Number(arr.join(&#039;&#039;)));\r\n}\r\n<\/pre>\n<p>\u6211\u5728 Firefox 11 \u4e0a\u7684\u7ed3\u679c\u662f\u5230 16 \u4f4d\u7684\u65f6\u5019\u5c31\u5df2\u7ecf\u5931\u771f\u4e86\u3002<\/p>\n<p>\u5982\u679c\u662f\u5c0f\u6570\u7684\u60c5\u51b5\uff1a<\/p>\n<pre class=\"brush: js\">\r\nvar arr = [&#039;9.&#039;];\r\nfor(var i = 0; i&lt; 21; i++) {\r\n  var str = arr.join(&#039;&#039;) + &#039;9&#039;;\r\n  push((i+1) + &#039; : &#039; + str, Number(str));\r\n  arr.push(&#039;9&#039;);\r\n}\r\n<\/pre>\n<p>\u540c\u6837\u5730\uff0c\u5c0f\u6570\u4f4d\u8fbe\u5230 15 \u4f4d\u65f6\u51fa\u73b0\u5931\u771f\u3002\u4e0a\u9762\u7684\u8bd5\u9a8c\u7528\u7684\u662f <a href=\"https:\/\/developer.mozilla.org\/en\/JavaScript\/Reference\/Global_Objects\/Number\" target=\"_blank\">Number() \u8fdb\u884c\u8f6c\u6362<\/a>\uff0c\u8fd9\u4e0e\u624b\u5199\u540c\u6837\u957f\u5ea6\u7684\u6570\u5b57\u6548\u679c\u662f\u4e00\u6837\u7684\u3002<\/p>\n<p>\u5e78\u8fd0\u7684\u662f\uff0c\u8fd9\u4e9b\u7cbe\u5ea6\u57fa\u672c\u591f\u7528\u4e86\u3002\u4f46\u5982\u679c\u54ea\u4f4d\u4ec1\u5144\u5e0c\u671b\u7528 JavaScript \u6765\u5904\u7406\u4e00\u4e9b\u9ad8\u7cbe\u5ea6\u65b9\u9762\u7684\u95ee\u9898\uff0c\u5c31\u5fc5\u987b\u5f97\u6ce8\u610f\u4e86\uff0c\u5176\u5b9e 15 \u4f4d\u5df2\u7ecf\u662f\u4e00\u9053\u574e\u4e86\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Javascript \u4e2d\u7684 Number \u662f\u4e2a\u795e\u5947\u7684\u7c7b\u578b\uff0c\u5b83\u6a21\u7cca\u4e86 \u6574\u5f62 \u548c \u6d6e\u70b9\u6570 \u4e4b\u95f4\u7684\u8fb9\u754c\uff0c\u5f53\u4f60\u62ff\u5230\u4e00\u4e2a &hellip; <\/p>\n<p class=\"link-more\"><a href=\"http:\/\/leegorous.net\/blog\/2012\/03\/21\/js-number-precision\/\" class=\"more-link\">\u7ee7\u7eed\u9605\u8bfb<span class=\"screen-reader-text\">\u201cNumber \u7684\u5931\u771f\u8fb9\u754c\u201d<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[102],"tags":[9],"_links":{"self":[{"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/posts\/1137"}],"collection":[{"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/comments?post=1137"}],"version-history":[{"count":4,"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/posts\/1137\/revisions"}],"predecessor-version":[{"id":1141,"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/posts\/1137\/revisions\/1141"}],"wp:attachment":[{"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/media?parent=1137"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/categories?post=1137"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/leegorous.net\/blog\/wp-json\/wp\/v2\/tags?post=1137"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}