return true actually returns undefined

Question

Heres my code. I don't really know what I'm doing wrong.

var arr = [{
   order_count: 1,
   order_date: "2015-10-10"

}, {
    order_count: 2,
    order_date: "2017-03-01"
}, {
    order_count: 3,
    order_date: '2017-04-10'
}];

function checkDay (date, maxDays){
   var flag = false;
   arr.forEach(function(element) {
     if (element.order_date === date && element.order_count >= maxDays)
     {
      flag = true;
      return true;
     }
   });
   if (!flag) {
    return false;
   }
}

console.log(checkDay('2017-04-10', 3));

because `checkDay` doesn't return anything when flag is true ... just `return flag` ... oh, and `return true` in forEach does not stop the forEach ... perhaps you want to look at array methods like `.some` or `.every` for loops that **can** terminate early — Jaromanda X, Feb 21 '18 at 00:44
https://stackoverflow.com/questions/34653612/what-does-return-keyword-mean-inside-foreach-function/34653650 — epascarello, Feb 21 '18 at 00:48

Isaac · Answer 1 · 2018-02-21T00:49:11.437

3

The return true inside your arr.forEach only breaks out of the current iteration inside the forEach (other iterations will continue to be executed), not the main function.

Change

if (!flag) {
 return false;
}

to

return flag;

edited Feb 21 '18 at 00:49

answered Feb 21 '18 at 00:46

Isaac

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Your statement is not right, there is NO way to break out of a forEach other than throwing an error. – epascarello Feb 21 '18 at 00:47
1

It doesn't break the entire forEach, it just breaks the current iteration. – Giovanni Lobitos Feb 21 '18 at 00:48
Clarified this. – Isaac Feb 21 '18 at 00:51

score 3 · Accepted Answer · answered Feb 21 '18 at 00:47

Use array.some method

function checkDay(date, maxDays) {
    return arr.some(element => element.order_date === date && element.order_count >= maxDays);
}

This will only loop until either all elements are processed and evaluated false, or finish looping once a true is returned - so, the behaviour is exactly as you expected

score 0 · Answer 3 · answered Feb 21 '18 at 00:47

You're not returning a value

function checkDay (date, maxDays) {
   var flag = false;

   arr.forEach(function(element) {
     if (element.order_date === date && element.order_count >= maxDays) {
      flag = true;
     }
   });

   return flag;
}

A better approach using the function some

function checkDay (date, maxDays) {
  return arr.some((element) => element.order_date === date && element.order_count >= maxDays);       
}

Resource

Array.prototype.some()

The some() method tests whether at least one element in the array passes the test implemented by the provided function.

return true actually returns undefined

3 Answers3

Resource