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i created an array and insert elements by array.push(). when i console.log(array) it gives me following out put output of console.log(array)
when i console.log(array[0]) it gives me undefined. why is happing and a blue i tag appear in picture which says "this value was evaluated on first expanding it may have changed since then in array javascript" what does means. please help me to understand the problem
here the full code
index.html =>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>zip reader</title>
</head>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js" integrity="sha512-894YE6QWD5I59HgZOGReFYm4dnWc1Qt5NtvYSaNcOP+u1T9qYdvdihz0PPSiiqn/+/3e7Jo4EaG7TubfWGUrMQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/jstree/3.2.1/themes/default/style.min.css" />
<script type="text/javascript" charset="utf8" src="https://cdnjs.cloudflare.com/ajax/libs/jstree/3.3.3/jstree.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jstree/3.2.1/jstree.min.js"></script>
<body>
<h3>Choose the local(s) zip file(s)</h3>
<input type="file" id="file" name="file" multiple /><br />
<div id="result_block" class="hidden">
<h3>Content :</h3>
<div id="result">
</div>
</div>
</body>
<script src="jszip.min.js"></script>
<script src="jszip-utils.min.js"></script>
<script src="app1.js"></script>
<script src="FileSaver.min.js"></script>
</html>
app1.js =>
var array = []
var contents = []
var $result = $("#result");
$("#file").on("change", function(evt) {
// remove content
$result.html("");
// be sure to show the results
$("#result_block").removeClass("hidden").addClass("show");
// Closure to capture the file information.
function handleFile(f) {
var $title = $("<h4>", {
text : f.name
});
var $fileContent = $("<ul>");
$result.append($title);
$result.append($fileContent);
var dateBefore = new Date();
JSZip.loadAsync(f) // 1) read the Blob
.then(function(zip) {
var dateAfter = new Date();
$title.append($("<span>", {
"class": "small",
text:" (loaded in " + (dateAfter - dateBefore) + "ms)"
}));
zip.forEach( function (relativePath, zipEntry) {
var y = zipEntry.name
array.push(y);
$fileContent.append($("<li>", {
text : zipEntry.name
}));
});
}, function (e) {
$result.append($("<div>", {
"class" : "alert alert-danger",
text : "Error reading " + f.name + ": " + e.message
}));
});
}
var files = evt.target.files;
for (var i = 0; i < files.length; i++) {
handleFile(files[i]);
}
console.log(array[0])
});
664
asked Oct 23 '25 15:10
When you console.log an object (including arrays), it isn't being serialized, and only a reference is passed to a console. When you expand it, this reference is used to check the state of this object.
Most probably what's happening is the following sequence:
console.log(array) // passes array reference to a consoleconsole.log(array[0]) // prints undefined immediatelyarray.push(...) // an actual array modificationPS.
It's reasonable to ask, what will happen, if the reference will become invalid due to any reason.
For browsers - it's simpler, since the console and JS program run under same parent process, browser is responsible for everything.
But if you'll ever try to debug Node process, which has the same API of passing the reference, you will face strange issues all over around, like this one: No debug adapter, can not send 'variables VSCODE
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