My result cannot read properties of undefined (reading 'length') in javascript

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I am trying to read the json document from php and convert it needed in js, but an error occurs. :
cannot read properties of undefined (reading 'length')
What went wrong? How can I loop the result below without using length ?

Here's the code:

What I have tried:

/*php */

$conn = db_connect();
$id = mysqli_fix_string( $conn, $id );

$Json_file = file_get_contents("files/sub/".$id."/".sub.json);
print( $json_file );

/*.js */
$.ajax({ url: "./sub/view_sub.php",
         type:"GET",
         data: { id: id },
         success: function( json ) {
            const result = JSON.parse( json );
            console.log(result.sub)
            console.log(result.sub[1]); // OK result is 'serg' 
            console.log(result.sub[2]); // OK result is 'dgf
            if( result.sub.length > 0 ){   <<== error
                 let i = 0;
                 for( const item of result.sub ){
                     foo_arr[id].input_text(i++, item );
                  }
               }
           }
});
              
// console result
>{1: 'serg', 2: 'dgf', 4: 'dfg ', 6: 'dfge ergre'}  <== console.log(result.sub)
uncaught typeError: Cannot read properties of undefined (reading 'length')

Posted 5-May-22 12:50pm

Chopin2001

Updated 5-May-22 22:08pm

v3

Add a Solution

2 solutions

Solution 1

Try using:

JavaScript

if( result.length > 0 )

Example:

JavaScript

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let length = fruits.length;

result returns:

Posted 5-May-22 14:04pm

Graeme_Grant

Comments

Chopin2001 5-May-22 20:16pm

This is my result /
console.log(result.sub)
>{1: 'serg', 2: 'dgf', 4: 'dfg ', 6: 'dfge ergre'}
if( result.length > 0 )
uncaught typeError: Cannot read properties of undefined (reading 'length')

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Richard Deeming · Accepted Answer · 2022-05-05T22:08:00

Quote:

This is my result /

JavaScript

console.log(result.sub)
{1: 'serg', 2: 'dgf', 4: 'dfg ', 6: 'dfge ergre'}

Your result is not an array; it's an object which happens to have numeric property names.

If you want to iterate over the properties of the object, you can use the Object.keys method[^]:

JavaScript

const subKeys = Object.keys(result.sub);
for (let i = 0; i < subKeys.length; i++) {
    foo_arr[id].input_text(i, result.sub[subKeys[i]]);
}