function.js

'use strict';


var parser = require('esprima');
var Type    = require('js-yaml').Type;


function resolveJavascriptFunction(data) {
  if (data === null) return false;

  try {
    var source = '(' + data + ')',
        ast    = parser.parse(source, { range: true });

    if (ast.type                    !== 'Program'             ||
        ast.body.length             !== 1                     ||
        ast.body[0].type            !== 'ExpressionStatement' ||
        (ast.body[0].expression.type !== 'ArrowFunctionExpression' &&
          ast.body[0].expression.type !== 'FunctionExpression')) {
      return false;
    }

    return true;
  } catch (err) {
    return false;
  }
}

function constructJavascriptFunction(data) {
  /*jslint evil:true*/

  var source = '(' + data + ')',
      ast    = parser.parse(source, { range: true }),
      params = [],
      body;

  if (ast.type                    !== 'Program'             ||
      ast.body.length             !== 1                     ||
      ast.body[0].type            !== 'ExpressionStatement' ||
      (ast.body[0].expression.type !== 'ArrowFunctionExpression' &&
        ast.body[0].expression.type !== 'FunctionExpression')) {
    throw new Error('Failed to resolve function');
  }

  ast.body[0].expression.params.forEach(function (param) {
    params.push(param.name);
  });

  body = ast.body[0].expression.body.range;

  // Parser's ranges include the first '{' and the last '}' characters on
  // function expressions. So cut them out.
  if (ast.body[0].expression.body.type === 'BlockStatement') {
    /*eslint-disable no-new-func*/
    return new Function(params, source.slice(body[0] + 1, body[1] - 1));
  }
  // ES6 arrow functions can omit the BlockStatement. In that case, just return
  // the body.
  /*eslint-disable no-new-func*/
  return new Function(params, 'return ' + source.slice(body[0], body[1]));
}

function representJavascriptFunction(object /*, style*/) {
  return object.toString();
}

function isFunction(object) {
  return Object.prototype.toString.call(object) === '[object Function]';
}

module.exports = new Type('tag:yaml.org,2002:js/function', {
  kind: 'scalar',
  resolve: resolveJavascriptFunction,
  construct: constructJavascriptFunction,
  predicate: isFunction,
  represent: representJavascriptFunction
});