locale.format()

locale.format(specifier)

Returns a new format function for the given string specifier. The returned function takes a number as the only argument, and returns a string representing the formatted number. The general form of a specifier is:

[​[fill]align][sign][symbol][0][width][,][.precision][type]

The fill can be any character. The presence of a fill character is signaled by the align character following it, which must be one of the following:

• > - Forces the field to be right-aligned within the available space. (Default behavior).
• < - Forces the field to be left-aligned within the available space.
• ^ - Forces the field to be centered within the available space.
• = - like >, but with any sign and symbol to the left of any padding.

The sign can be:

• - - nothing for positive and a minus sign for negative. (Default behavior.)
• + - a plus sign for positive and a minus sign for negative.
• ( - nothing for positive and parentheses for negative.
• (space) - a space for positive and a minus sign for negative.

The symbol can be:

• $ - apply currency symbols per the locale definition.
• # - for binary, octal, or hexadecimal notation, prefix by 0b, 0o, or 0x, respectively.

The zero (0) option enables zero-padding; this implicitly sets fill to 0 and align to =. 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 group separator, such as a comma for thousands.

Depending on the type, the precision either indicates the number of digits that follow the decimal point (types f and %), or the number of significant digits (types ​, e, g, r, s and p). If the precision is not specified, it defaults to 6 for all types except ​ (none), which defaults to 12. Precision is ignored for integer formats (types b, o, d, x, X and c). See precisionFixed and precisionRound for help picking an appropriate precision.

The available type values are:

• e - exponent notation.
• f - fixed point notation.
• g - either decimal or exponent notation, rounded to significant digits.
• r - decimal notation, rounded to significant digits.
• s - decimal notation with an SI prefix, rounded to significant digits.
• % - multiply by 100, and then decimal notation with a percent sign.
• p - multiply by 100, round to significant digits, and then decimal notation with a percent sign.
• b - binary notation, rounded to integer.
• o - octal notation, rounded to integer.
• d - decimal notation, rounded to integer.
• x - hexadecimal notation, using lower-case letters, rounded to integer.
• X - hexadecimal notation, using upper-case letters, rounded to integer.
• c - converts the integer to the corresponding unicode character before printing.
• ​ (none) - like g, but trim insignificant trailing zeros.

The type n is also supported as shorthand for ,g. For the g, n and ​ (none) types, decimal notation is used if the resulting string would have precision or fewer digits; otherwise, exponent notation is used. For example:

d3.format(".2")(42);  // "42"
d3.format(".2")(4.2); // "4.2"
d3.format(".1")(42);  // "4e+1"
d3.format(".1")(4.2); // "4"