# 格式化 > [Wiki](Home) ▸ \[\[API--中文手册\]\] ▸ \[\[核心函数\]\] ▸ **格式化** - 如发现翻译不当或有其他问题可以通过以下方式联系译者: - 邮箱：zhang\_tianxu@sina.com - QQ群：[D3数据可视化](http://jq.qq.com/?_wv=1027&k=ZGcqYF)205076374，[大数据可视化](http://jq.qq.com/?_wv=1027&k=S8wGMe)436442115 格式化数字是不经常用到的，只有在例如丑陋的"0.30000000000000004"出现在你的数轴标签上时，或者你想要使用固定精度将几千的数字组织为更加可读的形式，例如"$1,240.10"，再或者你可能只想展示一个特定的数字的显著位。D3使用标准的数字格式化使得一切变得简单，例如，创建一个用0补齐4位数字的函数，可以这样： ``` var zero = d3.format("04d"); ``` 现在，你就可以调用 zero 来很方便的格式化你的数字了： ``` zero(2); // "0002" zero(123); // "0123" ``` 当然，除了数字，D3还支持格式化和解析日期，逗号分隔字串。 ## Numbers [\#](#d3_format) d3.**format**(*specifier*) 返回给定的字符串（specifier）的格式化函数（等同于适用默认的美国英语语言环境的[locale.numberFormat](Localization#locale_numberFormat))。唯一的入参是数字，返回代表格式化数字的字符串。这个格式化规范模拟的是Python 3.1内置的格式化规范语言\[\[format specification mini-language|[http://docs.python.org/release/3.1.3/library/string.html#formatspec\]\]。规范（specifier）的通常格式如下](http://docs.python.org/release/3.1.3/library/string.html#formatspec%5D%5D%E3%80%82%E8%A7%84%E8%8C%83%EF%BC%88specifier%EF%BC%89%E7%9A%84%E9%80%9A%E5%B8%B8%E6%A0%BC%E5%BC%8F%E5%A6%82%E4%B8%8B): ``` [[fill]align][sign][symbol][0][width][,][.precision][type] ``` *fill*可以是任意字符，除了 “{“ 和 “}”，fill 由紧跟它的*align*选项标识。 *align*有三种选项： - ("<") 在可用的区域左对齐。 - (">") 在可用的区域右对齐（默认）。 - ("^") 在可用的区域居中。 *sign*可能是： - plus ("+") - 可以用于正数或负数。 - minus ("-") - 仅仅用于负数（默认）。 - space (" ") - 前面的空格应该用在正数前面，而减号必须用在负数！ *symbol*可能是： - currency ("$") - a currency symbol should be prefixed (or suffixed) per the locale. - base ("#") - for binary, octal, or hexadecimal output, prefix by "0b", "0o", or "0x", respectively. The "0" option enables zero-padding. The *width* defines the minimum field width. If not specified, then the width will be determined by the content. The *comma* (",") option enables the use of a comma for a thousands separator. The *precision* indicates how many digits should be displayed after the decimal point for a value formatted with types "f" and "%", or before and after the decimal point for a value formatted with types "g", "r" and "p". The available *type* values are: - exponent ("e") - use \[\[Number.toExponential|[https://developer.mozilla.org/en/JavaScript/Reference/Global\_Objects/Number/toExponential](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Number/toExponential)\]\]. - general ("g") - use \[\[Number.toPrecision|[https://developer.mozilla.org/en/JavaScript/Reference/Global\_Objects/Number/toPrecision](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Number/toPrecision)\]\]. - fixed ("f") - use \[\[Number.toFixed|[https://developer.mozilla.org/en/JavaScript/Reference/Global\_Objects/Number/toFixed](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Number/toFixed)\]\]. - integer ("d") - use \[\[Number.toString|[https://developer.mozilla.org/en/JavaScript/Reference/Global\_Objects/Number/toString](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Number/toString)\]\], but ignore any non-integer values. - rounded ("r") - round to *precision* significant digits, padding with zeroes where necessary in similar fashion to fixed ("f"). If no *precision* is specified, falls back to general notation. - percentage ("%") - like fixed, but multiply by 100 and suffix with "%". - rounded percentage ("p") - like rounded, but multiply by 100 and suffix with "%". - binary ("b") - outputs the number in base 2. - octal ("o") - outputs the number in base 8. - hexadecimal ("x") - outputs the number in base 16, using lower-case letters for the digits above 9. - hexadecimal ("X") - outputs the number in base 16, using upper-case letters for the digits above 9. - character ("c") - converts the integer to the corresponding unicode character before printing. - SI-prefix ("s") - like rounded, but with a unit suffixed such as "9.5M" for mega, or "1.00µ" for micro. The type "n" is also supported as shorthand for ",g". [\#](#d3_formatPrefix) d3.**formatPrefix**(*value*\[, *precision*\]) Returns the [SI prefix](http://en.wikipedia.org/wiki/Metric_prefix) for the specified *value*. If an optional *precision* is specified, the *value* is rounded accordingly using [d3.round](#d3_round) before computing the prefix. The returned prefix object has two properties: - symbol - the prefix symbol, such as "M" for millions. - scale - the scale function, for converting numbers to the appropriate prefixed scale. For example: ``` var prefix = d3.formatPrefix(1.21e9); console.log(prefix.symbol); // "G" console.log(prefix.scale(1.21e9)); // 1.21 ``` This method is used by d3.format for the `s` format. [\#](Formatting#d3_round) d3.**round**(*x*\[, *n*\]) Returns the value *x* rounded to *n* digits after the decimal point. If *n* is omitted, it defaults to zero. The result is a number. Values are rounded to the closest multiple of 10 to the power minus *n*; if two multiples are equally close, the value is rounded up in accordance with the built-in \[\[round|[https://developer.mozilla.org/en/JavaScript/Reference/Global\_Objects/Math/round](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Math/round)\]\] function. For example: ``` d3.round(1.23); // 1 d3.round(1.23, 1); // 1.2 d3.round(1.25, 1); // 1.3 d3.round(12.5, 0); // 13 d3.round(12, -1); // 10 ``` Note that the resulting number when converted to a string may be imprecise due to IEEE floating point precision; to format a number to a string with a fixed number of decimal points, use [d3.format](Formatting#d3_format) instead. ## Strings [\#](Formatting#d3_requote) d3.**requote**(*string*) Returns a quoted (escaped) version of the specified *string* such that the string may be embedded in a regular expression as a string literal. ``` d3.requote("[]"); // "\[\]" ``` ## Dates See the \[\[d3.time|Time-Formatting\]\] module.