string-generator

This is a simple template-based string generator. I wanted to generate random strings that met specific criteria for tests.

Why not use an existing package that does everything, like faker? If you need the complexity that comes with faker then by all means use it. But if you want to work with a very simple, template-driven API with no dependencies, then this might be helpful. It's simple, small, flexible, and moderately extensible.

Version 3 has major breaking changes.

Installing

You know the routine.

$ npm install --save-dev @bmacnaughton/string-generator@3

Usage

Here is documentation by example usage.

import Generator from '@bmacnaughton/string-generator';
const g = new Generator();
// get the tagFunction (bound to `g`) for template literals.
const gen = g.tagFunction();

gen`${'[A-F0-9]'}`;             // one random hex character
gen`${'=hex'}`;                 // one random lowercase hex character
gen`${'=HEX<10>'}`;             // 10 random uppercase hex characters
gen`${'=hex<4>}:${=hex<6>}:${=hex<2>'}`; // dead:beefca:fe (random)
gen`${'[ab]<10>'}`;             // 'abbbaabbba' (random)
gen`${'(this|that|else)<2>'}`;  // 'thiselse'
gen`${'"literal"<2>'}`;           // 'literalliteral'
gen`${'=hex<2:8>'}`;            // between 2 and 8 hex characters (inclusive)
gen`${'=hex<2|5|9>'}`;          // 2, 5, or 9 hex characters
gen`${`\` + someFunc()}`;

In all the above cases, the g.decode() function can be used on the string value with the ${..} construct, e.g., g.decode('=hex<2:8>') to convert the value directly. This can be useful if your code already uses a tag function.

import Generator from '@bmacnaughton/string-generator';
const g = new Generator();
// get the decode function (bound to `g`) for decoding literals
const decode = g.decodeFunction();

g.decode('${[A-F0-9]}');   // one random hex character
// or
decode('${[A-F0-9]}');

Options

The Generator constructor takes an options object.

• random - replace Math.random with this function that must have the same signature.
• codeWords - an object of word: function() pairs. code words are referenced using =word. if a code word is the same as a built-in code word (hex, HEX, etc.) then the built-in word is replaced. function() must return an indexable value, e.g., string or array.

Breaking changes from version 2

Version 3 uses ES modules. You must use an import statement or the import() function. There is only a default export, the Generator class.

Version 3 takes string-generator in a new direction. Version 2 embedded string-template-like patterns in a string. Version 3 embeds string patterns within string-templates that are executed by a tag-function (or by calling a decode function directly).

• v2: gen('${=alpha<20>}')
• v3: gen`${'=alpha<20>'}` or decode('=alpha<20>')

There are a number of other less significant changes.

• literal-specs use " or '
• it is possible to quote the first interpolated character with \ to avoid it being interpreted by string-generator.
• repeat-specs ranges use : instead of ,. Now <1:5> means the range 1 to 5.

Historical napkin scrawlings

I wanted a simple string generator. These are my original working notes.

/**
 * format:
 * '${pattern}${pattern}literal'
 *
 * pattern:
 * substitution-spec<count-spec>   // count-spec is optional
 *
 * substitution-spec:
 * [range-spec]
 * =code-word
 * (choice-spec)
 * literal
 *
 * count-spec:
 * count-range | count-oneof
 *
 * count-range:
 * min, max=min  // default when not present <1, 1>
 *
 * count-oneof:
 * n(|m)*
 *
 * range-spec
 * a-zA-Z0       // if - is desired must be first character
 *
 * code-word:
 * base58
 * alpha 'A-Za-z'
 * numeric '0-9'
 * alphanumeric 'A-Za-z0-9'
 * hex 'a-f0-9'
 * HEX 'A-F0-9'
 *
 * choice-spec:
 * this|that...
 *
 * literal-spec:
 * literal characters    // mostly useful for repeating
 *
 * characters not in a ${pattern} group are literal.
 */

todos

• ~~test suite~~
• ~~allow <n|m|o> syntax on count spec to choose one of the given lengths~~
• ~~convert to class~~
• ~~supply random number generator~~
• ~~options to supply own code-words~~
• ~~make basics.test iterate using optional random function.~~
• allow code-word functions to have arguments (wip)
• add base64 (convert given string to base64) like what syntax? @b64(arg)?