The id of the input seems is not WallSearch. Maybe you're confusing that name and id. They are two different properties. name is used to define the name by which the value is posted, while id is the unique identification of the element inside the DOM.
Other possibility is that you have two elements with the same id. The browser will pick any of these (probably the last, maybe the first) and return an element that doesn't support the value property.
The id of the input seems is not WallSearch. Maybe you're confusing that name and id. They are two different properties. name is used to define the name by which the value is posted, while id is the unique identification of the element inside the DOM.
Other possibility is that you have two elements with the same id. The browser will pick any of these (probably the last, maybe the first) and return an element that doesn't support the value property.
perhaps, you can first determine if the DOM does really exists,
function walkmydog() {
//when the user starts entering
var dom = document.getElementById('WallSearch');
if(dom == null){
alert('sorry, WallSearch DOM cannot be found');
return false;
}
if(dom.value.length == 0){
alert("nothing");
}
}
if (document.addEventListener){
document.addEventListener("DOMContentLoaded", walkmydog, false);
}
TypeError: Cannot read properties of undefined (reading 'length')
Uncaught TypeError: Cannot read properties of undefined (reading 'length') — DataTables forums
Help: “TypeError: Cannot read properties of undefined (reading ‘length’)
Cannot read properties of undefined (reading 'length')
Changing this if condition from this:
if (props.items.length === 0) {
To
if (!props.items?.length) {
Should work.
Similarly if using for places,you can check using ternary operator if length exists in array of places.
How? Because items could possibly be null or undefined from apis, so the length property on array might be missing.
Moreover, using ! Not operator would make this condition true if length of items is 0 or is null or undefined or any falsy value
The other answers are focusing on prop.items list but in your question you mention that you get the exception when trying to access the length of the places inside users.
You are getting the error message because some users may not have any places listed inside them, hence, no places list -> no length property.
To fix this, you need to check if the places list exists and then access its length:
placeCount={ user.places ? user.places.length : 0 }
Here, we use a ternary operator to check if user.places exists, then we use the length, else use zero.
Edit: As pointed out by Phil in the comments below, you can also use coalescing operator, which is much cleaner, like this:
placeCount={ user.places?.length ?? 0 }
The syntax simply translates as if user.places has a value for length, then use that value, else use zero as a default value.
I’m working in the p5.js editor and I’m having trouble with moving objects. I keep getting the error above, but I’m really not sure why.
https://editor.p5js.org/JadenRdcl/sketches/89YLI_gWD This is a really simple bouncing ball thing I made for an assignment a while back, and it worked fine. However, when I went back to see if it also had the error and it did, which is why I’m not sure what the problem is. The console also keeps saying things like “[p5.js, line 53353] Cannot read property of undefined” or “Error at line 53353 in _gridMap()” , and clicking on more info says “invalid file type” which makes me think I messed something up in the editor or on my device. Also, other programs I’ve made without moving objects work fine.
Any advice on how to fix this issue? Thanks in advance.
Receiving this error on one of my game files. All mods are turned off currently.
Currently running Version 11 Build 315
DnD5e 3.1.2
foundry.js:68326 Cannot read properties of undefined (reading 'length')
|| || ||fetch|@|foundry.js:68326| ||notify|@|foundry.js:68223| ||error|@|foundry.js:68260| ||_handleError|@|foundry.js:3468| ||(anonymous)|@|foundry.js:3450| ||value|@|socket.js:532| ||value|@|socket.js:459| ||L.emit|@|index.mjs:136| ||(anonymous)|@|manager.js:207| ||Promise.then (async)||| ||it|@|websocket-constructor.browser.js:5| ||value|@|manager.js:206| ||L.emit|@|index.mjs:136| ||value|@|index.js:131| ||value|@|manager.js:193| ||L.emit|@|index.mjs:136| ||value|@|socket.js:324| ||L.emit|@|index.mjs:136| ||value|@|transport.js:97| ||value|@|transport.js:89| ||ws.onmessage|@|websocket.js:69| ||Show less|
foundry.js:6629 TypeError: Cannot read properties of undefined (reading 'length')
at Preprocessor.advance (/data/application/re…processor.js:138:35)
at Tokenizer._consume (/data/application/re…zer/index.js:270:34)
at Tokenizer._runParsingLoop (/data/application/re…zer/index.js:221:29)
at Tokenizer.write (/data/application/re…zer/index.js:248:14)
at parseFragment (/data/application/re…dist/index.js:42:22)
at cleanHTML (/data/application/re…alidators.mjs:1:209)
at HTMLField.sanitizeHTMLField [as sanitize] (/data/application/re…tization.mjs:1:1235)
at Item._sanitizeFields (/data/application/re…document.mjs:1:7729)
at Item._sanitizeFields (/data/application/re…document.mjs:1:7956)
at Item.sanitizeUserInput (/data/application/re…document.mjs:1:7436)
|| || ||_onSubmit|@|foundry.js:6629| ||await in _onSubmit (async)||| ||_onSubmit|@|item-sheet.mjs:786| ||saveEditor|@|foundry.js:6773| ||onSave|@|item-sheet.mjs:410| ||_handleSave|@|prosemirror.js:19030| ||_onAction|@|prosemirror.js:19003| ||button.onclick|@|prosemirror.js:18504|