Alert and console.log continue to show the error message: 'Uncaught TypeError: Cannot read property ' ' of undefined

Encountering a Uncaught TypeError: Cannot read property 'valeurs' of undefined, however the alert() and console.log() functions are successfully displaying the data.

Below is the code snippet:

var item = document.getElementById('inputData').value;

$.ajax({
    url : 'php/modele.php',
    type : 'POST',
    data :{
        textValue : item
    },
    dataType : 'json',
    success : function(code_html, statut){

        var newhtml = '';

        console.log(code_html);
        
        for(var i = 0; i <= code_html.length; i++){

            alert(code_html[i]['valeurs']); // working but the error is pointing here. Line 21.

            newhtml += i+") "+code_html[i]['valeurs']+"<br>"; // not working
            console.log(code_html[i]['valeurs']); // working

        }

        alert(newhtml); //not displayed
        document.getElementById('container').innerHTML = newhtml;
        
    },
    error : function(resultat, statut, erreur){
        alert('error: '+erreur+' resultat: '+resultat);
    },
    complete : function(resultat, statut){ 

    }
 });

The alert() and console.log() functions are displaying the desired result. Alert is working console.log is working

However, the innerhtml is not updating due to the error, preventing the display of data on the HTML page.

Changing this line

newhtml += i+") "+code_html[i]['valeurs']+"<br>"; // not working
to
newhtml += i+") "+code_html[0]['valeurs']+"<br>"; // not working
resolves the issue and displays the value "bonjour" four times.

Answer №1

When working with arrays, it's important to remember that they start from index 0. So, if an array has a length of 4, the last element will have an index of 3. Therefore, instead of

for(var i = 0; i <= code_snippet.length; i++)

it is recommended to use

for(var i = 0; i < code_snippet.length; i++)
                ^^^

The incorrect display of values occurs because the loop runs one extra iteration beyond the scope of the array length.

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