ymd-h/format-js

format string with Python f-string or date command syntax

format.js

1. Usage

format.js provides two usage;

1. Python f-string like format
2. date command like format

Both usage have default formatter and user customization.

1.1 f-String like format

Pseudo Syntax: {index[:[[align]width][.precision]type]}

1.1.1 Default Usage

import { format } from "https://cdn.jsdelivr.net/gh/ymd-h/format-js@v1/format.js";

format("{0} + {1} = {2}", 1, 2, 1+2); // "1 + 2 = 3"
format("Precision: {0:.2f}", 1.78); // "Precision: 1.78"
format("Width: {0:4d}", 1); // "Width:   1"
format("Hex: {0:x}", 15); // "Hex: f"
format("Align: {0:<4d}", 1); // "Align: 1   "

1.1.2 Patch on Default

import { patch_default_format } from "https://cdn.jsdelivr.net/gh/ymd-h/format-js@v1/format.js";

const f = patch_default_format(
    { // key: (value: *, precision: number) => formatted_string
        "w": (value, precision) => value.toFixed(precision) + ` (${precision})`,
    }, // Patch for Format Handlers (optional)
    { // key: (value: string, width: number) => aligned_string
        "*": (value, width) => value.padStart(width, "*"),
    }, // Patch for Align (optional)
);

f.format("{0:.2w}", 1); // "1.00 (2)"
f.format("{0:.6w}", 1.25); // "1.000000 (6)"
f.format("{0:*6.2f}", 1); // "**1.00"

1.1.3 Custom Formatter from scratch

import { FStringLikeFormatter } from "https://cdn.jsdelivr.net/gh/ymd-h/format-js@v1/format.js";

const f = new FStringLikeFormatter(
    {
        ...
    }, // handlers
    {
        ...
    }, // align
    { defaultPrecision: 2 }, // options (optional)
);

f.format("My name is {0}.", "ymd-h");

1.2 date like format

1.2.1 Default Usage

import { format_date } from "https://cdn.jsdelivr.net/gh/ymd-h/format-js@v1/format.js";

format_date("%Y-%m-%d %H:%M:%S", new Date(2024, 2, 24, 18, 44, 52)); // "2024-03-24 18:44:52"
format_date("%T", new Date(2024, 2, 24, 18, 44, 52)); // "18:44:52"

1.2.2 Patch on Default

import { patch_default_formatformat_date } from "https://cdn.jsdelivr.net/gh/ymd-h/format-js@v1/format.js";

const f = patch_default_formatformat_date({
    "p": d => (d.getHours() < 12) ? "a.m." : "p.m.",
});

f.format("%p", new Date(2024, 2, 24, 18, 44, 52)); // "p.m."

1.2.3 Custom Formatter from scratch

import { DateLikeFormatter } from "https://cdn.jsdelivr.net/gh/ymd-h/format-js@v1/format.js";

const f = new DateLikeFormatter({
    "p": d => (d.getHours() < 12) ? "a.m." : "p.m.",
});

f.format("%p", new Date(2024, 2, 24, 18, 44, 52)); // "p.m."

2. Predefined Handlers / Aligns for Default Formatters

2.1 f-String like format

format	description
s	string (.toString())
b	binary number
c	unicode character (String.fromCodePoint())
d	integer
o	octal number
x	hexadecimal number. Use a-f for 10 to 15
X	hexadecimal number. Use A-F for 10 to 15
e	scientific notation. Use e for exponent
E	scientific notation. Use E for exponent
f	fixed point notation. Use nan / infinity
F	fixed point notation. Use NAN / INFINITY
%	percentage. multuply 100, fixed notation follewed by %

align	description
<	align left
^	align middle
> / (empty)	align right (default)

2.2 date like format

format	description
%y	year without century (2 digit)
%Y	year with century (4 digit)
%m	2 digit month (01 - 12)
%d	2 digit date (01 - 31)
%H	24 hour 2 digit hour (00 - 23)
%I	12 hour 2 digit hour (01 - 12)
%p	AM or PM
%M	2 digit minute (00 - 59)
%S	2 digit second (00 - 59)
%f	3 digit microsecond (000 - 999)
%s	Unix Time. Elapsed seconds from 1970-01-01 00:00:00 UTC
%T	Same as %H:%M:%S
%w	day of the week as number. Sunday is 0. (0 - 6)
%%	% (escaped)