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Editorial Team
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Asked: 2026-05-22T03:20:46+00:00

To learn JavaScript I am writing a small text editor Google Chrome extension. But

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To learn JavaScript I am writing a small text editor Google Chrome extension. But I keep getting this error: Cannot read property 'value' of undefined. It happens whenever tranquility.save(); is called, but not when tranquility.open(); which is weird because they are basically the same, just switched the sides. paper is just a <textarea>.

var tranquility = {
 paper: document.getElementById("paper"),
 lastOpenedPaper: localStorage.getItem("lastOpenedPaper"),

 listen: function() {
    this.paper.addEventListener("keyup", this.save, false);
 },

 save: function() {
    localStorage.setItem(this.lastOpenedPaper, this.paper.value);
 },

 open: function() {
    this.paper.value = localStorage.getItem(this.lastOpenedPaper);
 }
}

EDIT:

It is called after <textarea> is created (unless it has to be the entire DOM)

<body>
    <textarea id="paper"></textarea>
    <script src="../js/application.js"></script>
    <script>
        tranquility.listen();
    </script>
</body>
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1 Answer

  1. Editorial Team

    I got it working with two fixes

    1.) Write the script after loading of paper textarea. It was done by placing script at the end of body.

    2.) I found localStorage.setItem and localStorage.getItem should refer to the variable name like in http://hacks.mozilla.org/2009/06/localstorage/ . In your code lastOpenedPaper would refer to null value in begining so it won’t store value in that name so i tried replacing it with just. you can use other var name too or use varname directly as localStorage.setItem('anyvarname', this.paper.value);

    code:

    <script>
    var tranquility = {
     paper: document.getElementById("paper"),
     lastOpenedPaper: 'just',

     listen: function() {
        this.paper.addEventListener("keyup", this.save, false);
     },

     save: function() {
        localStorage.setItem(this.lastOpenedPaper, this.value);
     },

     open: function() {
        this.paper.value = localStorage.getItem(this.lastOpenedPaper);
     }
    }
</script>
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