javascript end of loop when an item of an array is undefined

Question

Please I am trying to display the firsts columns of a multidimensional array in JS but when the current item is undefined, the loop ends even when the following items follow the condition of the loop. this is my code.

for(var z = 0; z < 4; z++) {
     if(typeof(liste_des_points[z][0])!='undefined')
     alert(liste_des_points[z][0]);
 }

liste_des_points is actually an array built from the rows of a mysql table. N.B: I have tried to display these line independently and it works.

     alert(liste_des_points[0][0]);//this line display 0
     alert(liste_des_points[1][0]);//this line display 1
     alert(liste_des_points[2][0]);/*display anything because the value is      absent in the database*/
     alert(liste_des_points[3][0]);//this line display 3

Thanks

The loop only goes from 0 to 2.

Barmar
– Barmar

2017-11-09 00:33:07 +00:00
Commented Nov 9, 2017 at 0:33 — Barmar
– Barmar, Commented Nov 9, 2017 at 0:33
i.e. 3 < 3 === false

Jaromanda X
– Jaromanda X

2017-11-09 00:35:00 +00:00
Commented Nov 9, 2017 at 0:35 — Jaromanda X
– Jaromanda X, Commented Nov 9, 2017 at 0:35
sorry i meant z<4

atangopascall
– atangopascall

2017-11-09 05:04:16 +00:00
Commented Nov 9, 2017 at 5:04 — atangopascall
– atangopascall, Commented Nov 9, 2017 at 5:04
Please add console.log(liste_des_points) to the question.

Barmar
– Barmar

2017-11-09 16:55:21 +00:00
Commented Nov 9, 2017 at 16:55 — Barmar
– Barmar, Commented Nov 9, 2017 at 16:55

guest271314 · Accepted Answer · 2017-11-09 00:38:06Z

1

If liste_des_points[z] is empty, check for liste_des_points[z] as well before calling typeof()

for(var z = 0; z < 4; z++) {
  if(liste_des_points[z] && typeof(liste_des_points[z][0])!='undefined')
  alert(liste_des_points[z][0]);
}

answered Nov 9, 2017 at 0:38

guest271314

1

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8 Comments

guest271314 Over a year ago

@Barmar We do not know what liste_des_points[2] is, e.g., delete liste_des_points[2]

Barmar Over a year ago

He says the array is the results of a query. But I still say, if the element is deleted, alert(liste_des_points[2][0]) would report an error, not alert an empty value.

guest271314 Over a year ago

@Barmar Where does OP state that an empty value is alerted?

Barmar Over a year ago

He doesn't say that it gets an error when he does that alert.

guest271314 Over a year ago

@Barmar That is true as well. When tried to reproduce the missing code at OP used delete, which led to the Answer. If that is not the case, then OP can omit that portion of the expression.

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apsdehal · Accepted Answer · 2017-11-09 00:38:13Z

1

Try this:

for(var z = 0; z <= 3; z++) {
     if(typeof(liste_des_points[z][0]) !== 'undefined') {
         alert(liste_des_points[z][0]);
     }
 }

edited Nov 9, 2017 at 0:38

answered Nov 9, 2017 at 0:34

apsdehal

8452 gold badges10 silver badges27 bronze badges

6 Comments

Barmar Over a year ago

he doesn't want to stop the loop, he's saying that the loop is stopping when it shouldn't.

apsdehal Over a year ago

Oh, I will edit the question to be properly worded. Sorry for that, deleting this.

apsdehal Over a year ago

Well, can't delete now.

Barmar Over a year ago

Why can't you delete?

apsdehal Over a year ago

After comment, it says vote to delete. Anyways, I edited it.

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