Question

I have a function named uncompletedSteps():

function uncompletedSteps(completedSteps) {
    // completedSteps is an array
}

This function should examine completedSteps and return the index of all completedSteps elements that are not equal to true:

if (completedSteps[i] === true) {
    // add to return list
}

In other words, if have:

var completedSteps = [
    true,
    null,
    true
];

Then uncompletedSteps() should return [0, 2].

What should this uncompletedSteps() look like? (ECMAScript5 okay.)

Answer 1

Using reduce:

function uncompletedSteps(steps){
   return steps.reduce(function(memo, entry, i) { 
      return memo.concat(entry ? i : []);
   }, [])
}

Using forEach:

function uncompletedSteps(steps){
   var uncompleted = [];
   steps.forEach(function(entry,i) { 
      if(entry) uncompleted.push(i); 
   })
   return uncompleted;
}

Using map and filter

function uncompletedSteps(steps){
   return steps.map(function(entry, i) {
      return entry ? i : null;
   }).filter(function(entry) {
      return entry != null;
   });
}