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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"> <head> <title> new document </title> <meta name="generator" content="editplus" /> <meta name="author" content="" /> <meta name="keywords" content="" /> <meta name="description" content="" /> </head> <body><script language="javascript" type="text/javascript">var numStr = "";var charNine = "9";var maxLength = 20;for (var i=1; i<=maxLength; i++){ numStr += charNine; document.write(i, ": Str: ", numStr, " Num: ",parseInt(numStr), "<br />");}/*1: Str: 9 Num: 92: Str: 99 Num: 993: Str: 999 Num: 9994: Str: 9999 Num: 99995: Str: 99999 Num: 999996: Str: 999999 Num: 9999997: Str: 9999999 Num: 99999998: Str: 99999999 Num: 999999999: Str: 999999999 Num: 99999999910: Str: 9999999999 Num: 999999999911: Str: 99999999999 Num: 9999999999912: Str: 999999999999 Num: 99999999999913: Str: 9999999999999 Num: 999999999999914: Str: 99999999999999 Num: 9999999999999915: Str: 999999999999999 Num: 99999999999999916: Str: 9999999999999999 Num: 1000000000000000017: Str: 99999999999999999 Num: 10000000000000000018: Str: 999999999999999999 Num: 100000000000000000019: Str: 9999999999999999999 Num: 1000000000000000000020: Str: 99999999999999999999 Num: 100000000000000000000*/</script> </body></html>原文：https://www.cnblogs.com/nb123/p/12608974.html