Given an array, return one value at a time with each function call

Question

Given an array, return one value at a time with each function call. I need to make a function where I'm given an array of items and I need to return one value at a time until the last value.

I looked in on some answers and this is something that I thought would work but it's an infinite loop.

Am I close to a solution? Where am I going wrong?

function functionName() {
  
  var vals =
  ["shot_type","shot_height","shot_angle","framed","scene_depth"];
  for(var i=0; i<vals.length; i++) {
    functionName(vals[i]);
  }
}

functionName(); //expect 'shot type'
functionName(); //expect 'shot height'

you keep calling functionName.

Daniel A. White
– Daniel A. White

2018-01-18 21:00:18 +00:00
Commented Jan 18, 2018 at 21:00 — Daniel A. White
– Daniel A. White, Commented Jan 18, 2018 at 21:00
you should look at iterators.

Daniel A. White
– Daniel A. White

2018-01-18 21:00:36 +00:00
Commented Jan 18, 2018 at 21:00 — Daniel A. White
– Daniel A. White, Commented Jan 18, 2018 at 21:00

Jack · Accepted Answer · 2018-01-18 21:19:38Z

2

You could use iterators, but as I don't know about those I'd use a closure.

let functionName = () => {
  let i = -1;
  var vals = ["shot_type","shot_height","shot_angle","framed","scene_depth"];
  
  functionName = () => {
    i++;
    return vals[i];
  }
  
  return functionName();
}

console.log(functionName());
console.log(functionName());
console.log(functionName());

Here i is defined above the scope of the newly redefined functionName, and this is the reference to i that the new function retains.

edited Jan 18, 2018 at 21:19

answered Jan 18, 2018 at 21:10

Jack

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5 Comments

CRice Over a year ago

Hey, I like this solution but the snippet is skipping the first item? I notice that it is returning "shot_height" first, when it should be "shot_type"?

Jack Over a year ago

My bad, i needs to start at -1 as we're incrementing before the return. I've updated my answer.

CRice Over a year ago

Hmm, why not start at 0 and then do return vals[i++] instead of incrementing on the previous line?

Jack Over a year ago

Sure, that would work but I like to be verbose. Makes it easier for others to understand!

Mark Schultheiss Over a year ago

Pretty good, the inner function being an arrow function keeps the same scope

Jonas Wilms · Accepted Answer · 2018-01-18 21:06:20Z

0

  const functionName = (iter => () => iter.next().value)(vals.values());

This builds up an iterator and closures it in an IIFE, so you can iterate over it.

answered Jan 18, 2018 at 21:06

Jonas Wilms

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Comments

Mark Schultheiss · Accepted Answer · 2018-01-18 21:34:53Z

0

Not 100% sure how you want to "start over" but I went back to the top/0 one. Closure then call a function to get the value from that. Assumes at least 1.

var functionName = function() {
  var whichone = -1;
  var vals = ["shot_type", "shot_height", "shot_angle", "framed", "scene_depth"];
  this.getvalue = function() {
    whichone++;
    if (whichone === vals.length) {
      whichone = 0;
    }
    return vals[whichone];
  };
  return this;
}();

console.log(functionName.getvalue()); //expect 'shot type'
console.log(functionName.getvalue()); //expect 'shot height'
console.log(functionName.getvalue());// angle
console.log(functionName.getvalue());// framed
console.log(functionName.getvalue());//scene_depth
console.log(functionName.getvalue());// back to shot type

edited Jan 18, 2018 at 21:34

answered Jan 18, 2018 at 21:27

Mark Schultheiss

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Comments

CRice · Accepted Answer · 2018-01-18 21:10:20Z

-1

Arrays are iterators already, so if you can use iterators (es6+), then you can just do:

var vals = ["shot_type","shot_height","shot_angle","framed","scene_depth"];
const iter = vals[Symbol.iterator]();

console.log(iter.next().value);
console.log(iter.next().value);
console.log(iter.next().value);
// And so on.

// The iter.next() method returns an object: {value: any, done: boolean};
// When done is true, then there are no more values to get from the iterator.

answered Jan 18, 2018 at 21:10

CRice

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