javascript function, won't return to values?

Question

I'm trying to simplify a javascript function so it's more readable

Currently I'm trying to change this function below.

export default function generateSentimentLineGraphPoints(items) {
  /**
   * Generate array of 24 Zeros
   */
  let values = Array.apply(null, Array(24)).map(Number.prototype.valueOf, 0);
  const nOfEntries = Array.apply(null, Array(24)).map(
    Number.prototype.valueOf,
    1
  ); 
.....
}

to more simply use this function,

function generateTime() {
  /**
   * Generate array of 24 Zeros
   */
  let values = Array.apply(null, Array(24)).map(Number.prototype.valueOf, 0);
  const nOfEntries = Array.apply(null, Array(24)).map(
    Number.prototype.valueOf,
    1
  );
  return values, nOfEntries;
}

with,

function generateTime() {
  /**
   * Generate array of 24 Zeros
   */
  let values = Array.apply(null, Array(24)).map(Number.prototype.valueOf, 0);
  const nOfEntries = Array.apply(null, Array(24)).map(
    Number.prototype.valueOf,
    1
  );
  return values, nOfEntries;
}

This isn't working for some reason - i'm not sure why, it won't load the graph properly. Any ideas?

I think it needs more code to clarify. How are you using the old and new functions ? What graph are not loading ? Did you get any error message? Also, another thing is that JS does not allow returning multiple values, so you either return the 2 values as an object return {values, nOfEntries} and use destructing when calling the function: let {values, nOfEntries} = generateTime(), or return as an array return [values, nOfEntries] and caling it by: let [values, nOfEntries] = generateTime(). See this link for more info: javascripttutorial.net/javascript-return-multiple-values — Bao Huynh
– Bao Huynh, Commented Jul 11, 2021 at 10:00

T.J. Crowder · Accepted Answer · 2021-07-11 10:05:03Z

1

return values, nOfEntries; returns the value of nOfEntries, it doesn't return values at all. A JavaScript function can only return one thing. You're using the comma operator there, which evaluates its left-hand operand (values), throws away the result, then evaluates its right-hand operator (nOfEntries) and takes that result as the operation result.

To return multiple values, wrap them in an array or object:

return [values, nOfEntries];

or

return {values, nOfEntries};

Side note: That code to create an array filled with a given value is unnecessarily complex. Back in the day it probably should have just been a function that uses a loop, but these days you can use Array.prototype.fill:

let values = Array(24).fill(0);

edited Jul 11, 2021 at 10:05

answered Jul 11, 2021 at 9:59

T.J. Crowder

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2 Comments

LeCoda Over a year ago

Is there a simpler way to do the nOfEntries code as well?

T.J. Crowder Over a year ago

@LeCoda - The original code is exactly the same as for values but with 1 instead of 0, so...

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