Javascript: error cannot set property '...' of undefined

Question

Why is this line of JS code returning the error "cannot set property ... of undefined"?

document.forms["myForm"]["english_error"].textContent = "English sentence is required";

I am referencing the id of my div element correctly.

<input type="text" id="english" name="english" placeholder="English sentence" />
<div id="english_error" class="val_error"></div>

Assuming those elements are in myForm, not all elements with an ID will show up as properties of the form element. Mainly form controls will. — user1106925
– user1106925, Commented Nov 18, 2016 at 21:48
Possible duplicate of How to reference ID of DIV sending JavaScript call? — DDrake
– DDrake, Commented Nov 18, 2016 at 21:56

Marcs · Accepted Answer · 2016-11-19 01:08:30Z

1

Only form controls are mapped, basically only <input>, <textarea>, <select> tags:

var sentence = document.forms["myForm"]["english"];

Is an <input> tag so this works:

document.forms["myForm"]["english_error"].textContent = "English sentence is required";

english_error is normal <div> so doesn't work, you have to use:

document.getElementById("english_error").textContent = "English sentence is required";

And also by class name:

document.getElementsByClassName("val_error")[0].textContent = "English sentence is required";

answered Nov 19, 2016 at 0:37

Marcs

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