lines-builder

Tool and model to handle string lines and indentation.

Usage

To create a new lines-builder object:

import { lines } from "lines-builder";

const l = lines("Hello World\nThis is the 2nd line");
console.log(l);
// Hello World
// This is the 2nd line

The lines accepts an optional options object and any additional string (or lines-builder) as lines.

Options

Option	Type	Description	Default
indent	string|number	The indentation to use to indent the lines (exact string or the number of spaces).	null (no indentation)
indentEmpty	boolean	Whether the empty lines should still be indented.	false
skipFirstLevelIndent	boolean	Whether only the nested lines-builders should be indented.	false
skipEmpty	boolean	Whether empty lines should be added to the output string.	false
trimLeft	boolean	Can trailing white spaces be trimmed from the parsed lines.	true
trimRight	boolean	Can leading white spaces be trimmed from the parsed lines.	true
eol	string	The line-break to be used. If not set, it is determined based on the platform.	null

Append

You can append any lines, including a new line to the end (in place), passing any string (or lines-builder) as arguments to append :

l.append("3rd line", null, "4th line\nand 5th line");
console.log(l);
// Hello World
// This is the 2nd line
// 3rd line
// 
// 4th line
// 5th line

Prepend

You can prepend any lines, including new-line to the beginning (in place), passing any string (or lines-builder) as arguments to prepend :

l.prepend("This is the title", null, "And the 0th line");
console.log(l);
// This is the title
// 
// And the 0th line
// Hello World
// This is the 2nd line
// 3rd line
// 
// 4th line
// 5th line

Indent

You can set a global indentation to the lines added:

const l = lines({ indent: '--' }, "Hello World", "2nd line");
console.log(l);
// --Hello World
// --2nd line

By default, no indentation is set.

You can also set a number as the indentation. In this case, the given number of spaces will be used.

Trim

By default, lines-builder trims the leading and trailing whitespaces, but you can turn it off:

const l = lines({ trimLeft: false, trimRight: false }, "Hello World  ", "  2nd line\n  3rd line");
console.log(l);
// Hello World
//   2nd line
//   3rd line

Nesting

Lines-builder accepts another lines-builder instance instead of any string lines, to be able to nest it:

const nested = lines({ indent: '==' }, "1st nested", "2nd nested");
const parent = lines({ indent: '--' }, "1st parent", nested, "2nd parent");
console.log(parent);
// --1st parent
// --==1st nested
// --==2nd nested
// --2nd parent

By setting the skipFirstLevelIndent option, the lines-builder won't indent the direct lines of the lines-builder, only starting from the nested ones:

const nested = lines(, "1st nested", "2nd nested");
const parent = lines({ skipFirstLevelIndent: true, indent: '--' }, "1st parent", nested, "2nd parent");
console.log(parent);
// 1st parent
// --1st nested
// --2nd nested
// 2nd parent

Default options

As seen above, options can be set per each lines-builder, but if you want to use one set of options, per each lines-builder you will use, you can use the setDefaultOptions.

import { lines, setDefaultOptions } from "lines-builder";

setDefaultOptions({ indent: "__" });

const nested = lines("1st nested", "2nd nested");
const parent = lines("1st parent", nested, "2nd parent");
console.log(parent);
// __1st parent
// ____1st nested
// ____2nd nested
// __2nd parent

Note that the default options can be reset to the initial ones with the resetDefaultOptions.

EOL

To output/format the lines, the lines-builder will determine the appropriate EOL based on the platform used ( \r\n for Windows, \n for other OS). If you need to set explicitly what EOL to use, pass it in any options:

// IBM Mainframe EOL
const l = lines({ eol: "\025" }, "Hello", "World");
console.log(l);
// Hello\025World

Filtering

The filter method can be used to filter in place - either to keep or remove lines matching a specific pattern.

const l = lines("simple line", "# comment line", "other line");
// the following expression removes lines starting with #
l.filter(/^\s*#/, true);
console.log(l);
// simple line
// other line

If filtering needs to be done on a copy of the lines-builder, without touching the original one, the 3rd argument must be set to false:

const l = lines("simple line", "# comment line", "other line");
// the following expression removes lines starting with # and returns the result
const filtered = l.filter(/^\s*#/, true, false);

console.log(filtered);
// simple line
// other line

console.log(l);
// simple line
// # comment line
// other line

The filter function accepts either

1. a string, which will be converted to a case-insensitive RegExp
2. a RegExp, what will be used as it is
3. a type LineMatcher = (line: string, i: number) => boolean; function, what should return true in case of a match.

The filter function, based on the reverse parameter

1. if false, it keeps the line if the matcher is true; otherwise, it removes it
2. if true, it removes the line if the matcher is true; otherwise, it removes it

In the case of nested lines-builder, the same matcher and parameter are applied, and the nested one is kept if it contains any line after the filter.

Mapping

The map method can be used to map the lines in place, updating all the lines with a function.

const l = lines("line a", "line b", lines("nested line"));
// the following add level/index to each line
l.map((line: string, i: number, level: number) => `${level}/${i} - ${line}`);
console.log(l);
// 0/0 - line a
// 0/1 - line b
// 1/0 - nested line

If mapping needs to be done on a copy of the lines-builder, without touching the original one, the 2nd argument must be set to false:

const l = lines("line a", "line b", lines("nested line"));
// the following add level/index to each line
const mapped = l.map((line: string, i: number, level: number) => `${level}/${i} - ${line}`, false);

console.log(mapped);
// 0/0 - line a
// 0/1 - line b
// 1/0 - nested line

console.log(l);
// line a
// line b
// nested line

Copy

The copy method can be used to clone the lines-builder (including the nested lines, with the same options):

const l = lines("line a", "line b", lines("nested line"));
const copied = l.copy();

console.log(copied);
// line a
// line b
// nested line

console.log(l);
// line a
// line b
// nested line

Other

For detailed documentation see the TypeDocs documentation.

This package uses debug for logging, use lines-builder to see debug logs:

DEBUG=lines-builder node my-script.js