Recursion with pure function - Tasks Runner example

getTasks-v1.js

var input = ['dist'];

var config = {
  'dist': ['build', 'deploy'],
  'build': ['js', 'css', 'version-rev'],
  'js': ['lint','uglify'],
  'css': ['sass', 'css-min']
};

var tasks = [];

//hell
input.forEach(task => {
  if (config[task]){
    config[task].forEach(task =>{
      if (config[task]){
        config[task].forEach(task =>{
          if (config[task]){
            config[task].forEach(task =>{
              tasks.push(task);
            })
          } else {
            tasks.push(task);
          }
        })
      } else {
        tasks.push(task);
      }
    })
  } else {
    tasks.push(task);
  }
})

console.log(tasks);

getTasks-v2.js

var input = ['dist'];

var config = {
  'dist': ['build', 'deploy'],
  'build': ['js', 'css', 'version-rev'],
  'js': ['lint','uglify'],
  'css': ['sass', 'css-min']
};

//external state
var tasks = []; 

getTasks(input);

//hard to test
function getTasks(input){
  input.forEach(task => {
    if (config[task]){
      getTasks(config[task]);
    } else {
      tasks.push(task);
    }
  });
}

console.log(tasks);

getTasks-v3.js

var input = ['build'];

var config = {
  'build': ['js', 'css', 'version-rev'];
  'js': ['lint','uglify'],
  'css': ['sass', 'css-min']
};

var tasks = getTasks(config, input, []);

//pure function
function getTasks(config, input, initial){
  return input.reduce((prev, next) => {
    if(config[next]){
      return getTasks(config, config[next], prev);
    } else {
      return prev.concat(next);
    }
  }, initial);
}

console.log(tasks);