Business rules as text with NEWMACRO()

Total.js 5 · total5@0.0.19 macrosrulesscripting Executed against Total.js 5

NEWMACRO(text, [nocompile], [isasync]) turns a few lines of a small language into a function function(model, helpers). It is meant for rules that change more often than the code: a discount, a price, a permission check, a validation that someone who does not write JavaScript maintains in a file or in a database.

The language, as it was checked:

IF condition, ELSE IF condition, ELSE and FI (the end of the condition) work as in a text-based rule. Conditions use >, <, >=, <=, = and AND / OR.
RETURN value ends the macro with a value. YES and NO (also TRUE, FALSE, OK) are booleans, text between quotes is text and numbers are numbers.
A word is a property of the model, written in lower case: age reads model.age, and total = price * qty writes model.total.
NAME(arguments) calls a helper, the function with that name (lower case) in the helpers object you pass; inside it this is the model. With isasync set to true the macro is an async function and awaits the helpers.
#name is a temporary variable of the run: #temp = num + 1 and RETURN #temp.
Use names of several letters: a property or a variable of one letter was not recognised in the checks.

NEWMACRO() compiles the text with new Function, so a macro is code: only compile text that you wrote or that a trusted person maintains, never text that a visitor sent. With nocompile set to true it returns the JavaScript that it generates instead of the function, which is useful to see what a rule does.

controllers/rules.js

const helpers = {
	percent: function(value, rate) {
		return value * rate / 100;
	}
};

const age = NEWMACRO("IF age >= 18\n\tRETURN 'adult'\nELSE\n\tRETURN 'minor'\nFI");

const level = NEWMACRO("IF points > 100\n\tRETURN 'gold'\nELSE IF points > 50\n\tRETURN 'silver'\nELSE\n\tRETURN 'bronze'\nFI");

const access = NEWMACRO("IF active AND score >= 5\n\tRETURN yes\nFI\nRETURN no");

const total = NEWMACRO("total = price * qty\nIF qty >= 10\n\ttotal = total - PERCENT(total, 10)\nFI\nRETURN total");

const temporary = NEWMACRO("#next = count + 1\nRETURN #next");

const slow = NEWMACRO("RETURN LOOKUP(code)", false, true);

exports.install = function() {
	ROUTE('POST /rules/', rules);
	ROUTE('GET /source/', source);
};

async function rules($) {
	const model = $.body;
	$.json({
		age: age(model, helpers),
		level: level(model, helpers),
		access: access(model, helpers),
		total: total(model, helpers),
		model_total: model.total,
		temporary: temporary(model, helpers),
		slow: await slow(model, { lookup: async code => 'found ' + code })
	});
}

function source($) {
	$.plain(NEWMACRO("IF points > 100\n\tRETURN 'gold'\nFI", true));
}