Using the push method on a global object array will replace all existing values within the array

Question

Using the push method on a global object array will replace all existing values within the array

After researching various solutions to this issue, I have not been successful in implementing the commonly suggested fix. The variable evtList holds a collection of global objects labeled as "Event". Previous discussions advised creating a local object ("newEvent") within a loop, setting its properties, and then adding it to the global array. Despite following these steps, I have observed that modifying the newEvent object's elements results in all objects within the global array being updated with the same values before the addition operation. What am I overlooking here?

var i = 0;
var nextTime = new Date();

while (evtList[i].evtTime < dayEnd) {
    i++;
    var newEvent = new Event;
    var milliSecs = (evtList[i-1].evtTime).getTime() + gaussian(arrStations[0].mean, arrStations[0].stdDev);
    nextTime.setTime(milliSecs);
    newEvent = ({value: 1, station: 0, evtTime: nextTime});

    evtList.push(newEvent);
}

javascript arrays push

Answer 1

Answer №1

When working with JavaScript, it's important to note that the var keyword does not establish block-level scope, but rather function-level scope. This means that variables like newEvent are not limited to the for loop they are declared in, but rather belong to the function body or the global scope if not inside a function.

In your code, when you use push to add objects to your evtList, you run into an issue where all the evtTime properties reference the same Date object. As a result, any changes made to one evtTime affect all the others because they are essentially pointing to the same object.

To resolve this, you should create a new Date object for each of your objects as shown in the code snippet below:

var newEvent;
var milliSecs;
var nextTime;
var i = 0;

while (evtList[i].evtTime < dayEnd) {
  i++;
  nextTime = new Date;
  milliSecs = (evtList[i - 1].evtTime).getTime() + gaussian(arrStations[0].mean, arrStations[0].stdDev);
  nextTime.setTime(milliSecs);
  newEvent = ({
    value: 1,
    station: 0,
    evtTime: nextTime
  });

  evtList.push(newEvent);
}

Furthermore, it seems that the newEvent object pushed to evtList is not of the expected type Event because it is being overwritten by a plain JavaScript object. You can correct this by explicitly setting the properties of the Event object, as shown in the following code snippet:

newEvent.value = 1;
newEvent.station = 0;
newEvent.evtTime = nextTime;

Alternatively, you could pass these properties to your Event constructor for better organization and consistency in your code.

Answer 2

When working with JavaScript, it's important to note that the var keyword does not establish block-level scope, but rather function-level scope. This means that variables like newEvent are not limited to the for loop they are declared in, but rather belong to the function body or the global scope if not inside a function.

In your code, when you use push to add objects to your evtList, you run into an issue where all the evtTime properties reference the same Date object. As a result, any changes made to one evtTime affect all the others because they are essentially pointing to the same object.

To resolve this, you should create a new Date object for each of your objects as shown in the code snippet below:

var newEvent;
var milliSecs;
var nextTime;
var i = 0;

while (evtList[i].evtTime < dayEnd) {
  i++;
  nextTime = new Date;
  milliSecs = (evtList[i - 1].evtTime).getTime() + gaussian(arrStations[0].mean, arrStations[0].stdDev);
  nextTime.setTime(milliSecs);
  newEvent = ({
    value: 1,
    station: 0,
    evtTime: nextTime
  });

  evtList.push(newEvent);
}

Furthermore, it seems that the newEvent object pushed to evtList is not of the expected type Event because it is being overwritten by a plain JavaScript object. You can correct this by explicitly setting the properties of the Event object, as shown in the following code snippet:

newEvent.value = 1;
newEvent.station = 0;
newEvent.evtTime = nextTime;

Alternatively, you could pass these properties to your Event constructor for better organization and consistency in your code.

Using the push method on a global object array will replace all existing values within the array

Answer №1

Similar questions

Utilize AngularJS to create a concealed input field

Guide on dragging and dropping without losing the item, allowing for continuous drag and drop functionality

Expand the HTML Template and Resize Children to Fit the Window

Why do confirm or alert boxes in Safari on Windows require a double click?

Issues with PHP server handling JSON files

Encountering the 'navigator is not defined' error when attempting to generate a Next JS build

Extract data from a CSV table stored in a variable using node.js

Sending multiple objects using Ajax and fetching them in PHP

The Rtk query function does not generate endpoints

Trouble arises when accessing GET form in php/Ajax

What is the best way to ensure that the input submit element is only visible after the input checkbox element has been checked?

Tips for efficiently importing a file or folder that is valuable but not currently in use

Tips on organizing and designing buttons within a canvas

React not displaying wrapped div

Saving base64 encoded pdf on Safari

Module exists; however, command could not be located

Google Chrome is unable to process Jquery JSON .each() function

Guide to creating scroll-based animations for a Div element

Creating a specialized Angular directive for handling input of positive numbers

Leveraging the CSS-Element-Queries Library for emulating the functionality of CSS media queries