JavaScript - Cannot Set Property of Undefined

JavaScript - cannot set property of undefined

you never set d[a] to any value.

Because of this, d[a] evaluates to undefined, and you can't set properties on undefined.

If you add d[a] = {} right after d = {} things should work as expected.

Alternatively, you could use an object initializer:

d[a] = {
    greetings: b,
    data: c
};

Or you could set all the properties of d in an anonymous function instance:

d = new function () {
    this[a] = {
        greetings: b,
        data: c
    };
};

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If you're in an environment that supports ES2015 features, you can use computed property names:

d = {
  [a]: {
    greetings: b,
    data: c
  }
};

TypeError: Cannot set properties of undefined (setting '0')'----Array assignment

Whenever the value of i becomes 1, inside the inner loop it is setting the value to n[i][j], which is n[1][0], here n[1] is undefined and it is accessing the 0th index value of undefined, that is the reason of the error.

the first iteration works fine because there is already an empty array in the 0th index (when i = 0).

here you can try doing this

let n = []
let index = 0
for (let i = 0; i < r; i++) {
    n[i] = [];
    for (let j = 0; j < c; j++) {
        n[i][j] = arr[index];
        index++;
    }
}

return n;

TypeError: Cannot set properties of undefined (setting 'duration')

What is happening is that you are trying to access an item in the list using the index listOfSelectedQuestions[index] but the item doesn't exists.

What you can do is add an object to the index if it doesn't exists

if (listOfSelectedQuestions[index]) {
  // item exists, so only modify the property
  listOfSelectedQuestions[index][name] = value;
} else {
  // item doesn't exists, so add a new object entirely
  listOfSelectedQuestions[index] = {
    [name]: value
  }
}

Javascript cannot set property 0 of undefined

You are missing the array initialization:

var array = [];

Taking this into your example, you would have:

var array = []; //<-- initialization herefor(var i = 1; i<10;i++) {    array[i]= Math.floor(Math.random() * 7);}console.log(array);

TypeError: Cannot set properties of undefined (setting 'message') in Vue

alert in undefined because appController.js doesn't export alert. Based on the code you shared, it exports a data method which has the alert.

So to access it, it would look something like...

import {data} from './appController.js';
const { alert } = data();

export default {
  methods: {
    loginFunc() {
      alert.message = "Test 2";
    }
  }
}

This would make it accessible, but not sure if that's what you want.

If you want to be able to edit a value from anywhere you would use a a global store. To make it reactive you could use ref or reactive but only with composition API but also using a global store like vuex, pinia or oeve vue observable. If you have a single alert that watches for that globally-accessible and reactive value, it would then update.

Note that even in your current example, the value appears not to be globally accessible nor reactive, so you would have to manage reactivity and pass it to the component.

If you're using vue3, you can have a look at this sample via vue SFC playground. Note that it's using reactive to manage a "singleton" global state and the alert component is always present, but the visibility is handled internally.

TypeError: Cannot set property 'usingClientEntryPoint' of undefined

As you are mocking react-dom and since createRoot is exposed from react-dom/client, you would need to do this way instead:

jest.mock("react-dom/client", () => ({ 
  createRoot: jest.fn().mockImplementation(() => ({
    render: jest.fn() 
  }))
}));

describe('Application root', () => {
  it('should render without crashing', () => {
    // render your app here
    expect(renderFn).toHaveBeenCalled();
  });
});

Uncaught TypeError: Cannot set properties of undefined on Javascript

If you run this code snippet JSFiddle:

var arry = [[[[]]]],
    i1 = 0,
    i2 = 0,
    intervalRate = 1000;
    turn = 0, a = 10, b = 5;

for(i = 0; i < 2; i++) arry.push([]);

console.log(arry);
console.log(arry[0][0]);
console.log(arry[1][0]);

Console output is:

[[[[]]], [], []] // 3 root elements
[[]] // 1st child of array[0];
undefined // 1st child of array[1]

So to fix, you would have to initialize all elements of all array dimensions, but the last one. If you use arry[turn][i1][i2], you have to cover (initialize upfront) for all possible values of turn and i1 to avoid error. Or, even better, to change the approach/algorithm completely. Find cleaner way.

JS - cannot set property of undefined

req.client.states is undefined, that's why you're getting error. Why are you setting it anyway, since you're not using that value anywhere later on?

TypeError: Cannot set property 'data_id' of undefined

data[i] is undefined so

Simply Change

data[i] = {};
data[i]['data_id'] = data_id;

$('#btn_valid').click(function(){
    var data = new Array();    var data_id;    var data_picture;    var data_title;    var data_p_picture;    var data_p_title;    var data_s_picture;    var data_s_title;    var data_reaction;    var data_datetime;    var i = 0;

    $('.cbx_ac:checked').each(function(){
      data_id = $(this).attr('data-id');      data_picture = $(this).attr('data-picture');      data_title= $(this).attr('data-title');      data_p_picture = $(this).attr('data-p_picture');      data_p_title = $(this).attr('data-p_title');      data_s_picture = $(this).attr('data-s_picture');      data_s_title = $(this).attr('data-s_title');      data_reaction = $(this).attr('data-reaction');      data_datetime = $(this).attr('data-datetime');
      console.log(data_id); // I Get a value here ( 2564115647_15498456665 )       data[i] = {};      data[i]['data_id'] = data_id;  //Error here :  Uncaught TypeError: Cannot set property 'data_id' of undefined      i++;   
    })    console.log(data);  })

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><input type="button" class="btn" id="btn_valid" value="Click Me" /><input type="checkbox" data-id="data-id" data-picture="pic1" data-title="title1" id="scales" class="cbx_ac" name="feature"               value="scales" checked />

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