Javascript : Undefined before an array

Question

i'm having trouble with a little code i'm writing in javascript which is supposed to return a table with a column for month and a column for profits. Everything is okay except it seems that i got a undefined value out of nowhere. Here's the code :

"use strict";

var i, mois, ventes, a, b;
mois=["Janvier","Fevrier","Mars","Avril","Mai","Juin","Juillet","Aout","Septembre","Octobre","Novembre","Decembre"];
ventes=[120,500,350,400,600,890,450,100,250,300,650,450];

function Fventes(a, b) {
    for (i=0; i<12; i++) {
    document.write('<tr><td>', a[i],'</td><td>',b[i],'</td></tr>');
    }
}
document.write('<table><thead><td>Tableau des ventes</td></thead><tbody>');
document.write(Fventes(mois, ventes));
document.write('</tbody></table>');

The undefined value appears before the 1st document write, as if i was calling the value of an empty variable.

Try to avoid document.write and consider using DOM Methods instead; i.e. parent_node.appendChild(table_root_node) — Paul S.
– Paul S., Commented Apr 13, 2015 at 0:10

Dave Lasley · Accepted Answer · 2015-04-13 00:06:29Z

3

It's because you're document.writing a function, which returns undefined implicitly due to the rules of Javascript. Inside of that function are the document.writes you really wanted. Try:

"use strict";

var i, mois, ventes, a, b;
mois=["Janvier","Fevrier","Mars","Avril","Mai","Juin","Juillet","Aout","Septembre","Octobre","Novembre","Decembre"];
ventes=[120,500,350,400,600,890,450,100,250,300,650,450];

function Fventes(a, b) {
    for (i=0; i<12; i++) {
        document.write('<tr><td>', a[i],'</td><td>',b[i],'</td></tr>');
    }
}
document.write('<table><thead><td>Tableau des ventes</td></thead><tbody>');
Fventes(mois, ventes);
document.write('</tbody></table>');

Fiddle: https://jsfiddle.net/zsh18999/

answered Apr 13, 2015 at 0:06

Dave Lasley

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Comments

Jose Ricardo Bustos M. · Accepted Answer · 2015-04-13 00:07:26Z

1

you should write:

document.write('<table><thead><td>Tableau des ventes</td></thead><tbody>');
Fventes(mois, ventes);
document.write('</tbody></table>');

answered Apr 13, 2015 at 0:07

Jose Ricardo Bustos M.

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Comments

Magador · Accepted Answer · 2015-04-13 00:08:00Z

1

Calling document.write(Fventes(mois, ventes)); actually writes "undefined" because calling Fventes(mois, ventes) return undefined. you should write:

"use strict";

var i, mois, ventes, a, b;
mois=["Janvier","Fevrier","Mars","Avril","Mai","Juin","Juillet","Aout","Septembre","Octobre","Novembre","Decembre"];
ventes=[120,500,350,400,600,890,450,100,250,300,650,450];

function Fventes(a, b) {
    for (i=0; i<12; i++) {
    document.write('<tr><td>', a[i],'</td><td>',b[i],'</td></tr>');
    }
}
document.write('<table><thead><td>Tableau des ventes</td></thead><tbody>');
Fventes(mois, ventes);
document.write('</tbody></table>');

answered Apr 13, 2015 at 0:08

Magador

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