[Javascript] Intro to Recursion - Detecting an Infinite Loop

When using recursion, you must be mindful of the dreaded infinite loop. Using the recursive function that we’ve built up over the previous lessons, we look at how a simple duplicated configuration item could cause chaos for our program as it has no context of which items it has previously seen. We fix this problem by introducing a parents array, which can keep track of which top-level commands have already been accessed.

Previous:

let input, config;

input = ['dist'];

config = {
  "dist": ["build", "deploy"],
  "build": ['js', 'css', 'vender'],
  "js": ['babel', 'ng-Annotate', "uglify"],
  "css": ["sass", "css-min"]
};

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

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(res);

----------

Code:

let input, config;

input = ['dist'];

config = {
  "dist": ["build", "deploy"],
  "build": ['js', 'css', 'vender', 'dist'],
  "js": ['babel', 'ng-Annotate', "uglify"],
  "css": ["sass", "css-min"]
};

var res = getTasks(config, input);

function getTasks(config, input, initial, parent){

  initial = initial || [];
  parent = parent || [];

  return input.reduce((prev, next)=>{

    if(parent.indexOf(next) > -1){
      console.log('infinite loop detected!');
      return prev;
    }

    if(config[next]){
      return getTasks(config ,config[next], prev, parent.concat(next));
    }else{
      return prev.concat(next);
    }
  }, initial);
};

console.log(res);