I am getting Error from For Loop function in Javascript

Question

this is a function to call SELECT element values. but i am facing an error. code is here.

function get_s_val(){
var foo = all_categories_1;
var ov1 = "";

    for(m=0;m<=foo.length;m++){
        ov1 += foo[m].value+',';
    }

console.log(ov1);
var tme=setTimeout("get_s_val()", 1000);
}
get_s_val();

it shows an error like "Uncaught TypeError: Cannot read property 'value' of undefined"

but when i do some littel changes it works.. like

function get_s_val(){
var foo = all_categories_1;
var ov1 = "";

    //for(m=0;m<=foo.length;m++){
        ov1 += foo[0].value+',';
    //}

console.log(ov1);
var tme=setTimeout("get_s_val()", 1000);
}
get_s_val();

i dont know that where i am wrong to write the code.

Why don't you use var for the loop variable, why do you pass a string to setTimeout? — ThiefMaster
– ThiefMaster, Commented Oct 28, 2011 at 11:24

karim79 · Accepted Answer · 2011-10-28 11:23:14Z

2

Modify your loop condition to run while the iterator is less than the length of the array, or you'll get undefined when you hit the non-existent element at index foo.length:

for(var m=0;m<foo.length;m++){
    ov1 += foo[m].value+',';
}

...and always declare variables with the var keyword, or bad things will happen, and JSLint will whine about it (and rightly so, but that's another topic).

answered Oct 28, 2011 at 11:23

karim79

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3 Comments

Shahrukh Over a year ago

Thanks Karim. it works. but tell me 1 thing, is "=<" or ">=" wrong thing to use.

karim79 Over a year ago

If you want to iterate over all elements of an array, then yes. The first element of an array is at index 0, so the last item is at total number of elements - 1. Hope that's clear.

Shahrukh Over a year ago

yeh Karim, i know that rule.. but i just now understand that where was the problem. thanks alot.

pimvdb · Accepted Answer · 2011-10-28 11:23:29Z

1

function get_s_val(){
    var foo = all_categories_1;
    var ov1 = "";

        for(var m = 0; m < foo.length; m++){ // use var, and only loop from e.g.
                                             // 0 to 2 when the length is 3, so <,
                                             // not <=
            ov1 += foo[m].value+',';
        }

    console.log(ov1);

    setTimeout(get_s_val, 1000); // don't use a string, just pass the function.
                                 // Plus, the variable is nowhere accessible so
                                 // you can drop storing it
}

get_s_val();

Anyway, if you simply want to join the array's elements into a string with , as delimiter, why not do:

console.log(foo.join());

answered Oct 28, 2011 at 11:23

pimvdb

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1 Comment

Shahrukh Over a year ago

Thanks pimvdb for your answer and for join() function.

Hammerite · Accepted Answer · 2011-10-28 11:24:26Z

0

At the top of the for loop, m<=foo.length; should instead be m<foo.length;.

answered Oct 28, 2011 at 11:24

Hammerite

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1 Comment

Shahrukh Over a year ago

Thanks Hammerite for answering me.

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