How does setting 0 as the initial element of an array prevent the execution of a "for" loop in JavaScript?

Question

How does setting 0 as the initial element of an array prevent the execution of a "for" loop in JavaScript?

Take a look at the JavaScript code snippet below:

var words = delIdx = [0, 1, 2, 3];
for(let i=0; delIdx[i]; i++) {
  console.log('DELIDX: ', delIdx[i]);
}

for(let i=0; words[i]; i++) {
  console.log('Word: ', words[i]);
}

The arrays words and delIdx are being used in the FOR loops to control the execution of the code. However, when the first element of the array is set to 0, the loops do not work as expected and do not enter the loop at all.

Changing the array's values to

var words = delIdx = [2, 3, 4, 5]

resolves the issue and the loops work correctly.

Have you encountered this problem before? Is it a bug in JavaScript?

This behavior was observed in Node.js v5.3.0 and FireFox 44.0.2 console.

Any thoughts or insights on this?

Thank you.

javascript arrays

Answer 1

Answer №1

When implementing a for loop in JavaScript, the condition in the middle is considered the predicate:

If the condition evaluates to true, the loop will continue executing
If the condition evaluates to false, the loop will stop

In this scenario, you have provided 0 as the condition, which is evaluated as false, resulting in the loop not executing.

Answer 2

When implementing a for loop in JavaScript, the condition in the middle is considered the predicate:

If the condition evaluates to true, the loop will continue executing
If the condition evaluates to false, the loop will stop

In this scenario, you have provided 0 as the condition, which is evaluated as false, resulting in the loop not executing.

Answer 3

Answer №2

The loop is not functioning properly because when it encounters a value of 0, it evaluates to false. Removing the 0 from the array allows the loop to work correctly. You can also iterate through the array using the following code:

var numbers = myNumbers = [1, 2, 3, 4];
for(var i=0; i<myNumbers.length; i++) {
  console.log('MyNumber: ', myNumbers[i]);
}

for(var i=0; i<numbers.length; i++) {
  console.log('Number: ', numbers[i]);
}

Answer 4

The loop is not functioning properly because when it encounters a value of 0, it evaluates to false. Removing the 0 from the array allows the loop to work correctly. You can also iterate through the array using the following code:

var numbers = myNumbers = [1, 2, 3, 4];
for(var i=0; i<myNumbers.length; i++) {
  console.log('MyNumber: ', myNumbers[i]);
}

for(var i=0; i<numbers.length; i++) {
  console.log('Number: ', numbers[i]);
}

How does setting 0 as the initial element of an array prevent the execution of a "for" loop in JavaScript?

Answer №1

Answer №2

Similar questions

Utilizing data from an external JavaScript file in an Express application

Using TypeScript and the `this` keyword in SharePoint Framework with Vue

Showing a collection of articles on a webpage using Nuxt/content - Step by step guide

Using a custom module in node.js to retrieve data from a mysql database

Stop processing the current websocket connection once a new websocket request is received

Scrolling to the complete height of a div using scrollTop

having difficulty in transmitting json data using ajax

Bootstrap Carousel is unable to display any items as the count returns zero

What is the best way to determine the size of a char array?

Obtain a specific element in Puppeteer JS by utilizing the waitForSelector function to detect when its class name changes

What could be causing the vue-property-decorator @Emit to malfunction in my Vue TypeScript file?

Leveraging PapaParse for CSV file parsing in a React application with JavaScript

unable to navigate to next or previous page in react-bootstrap-table2-paginator

Deciphering Google location data using JavaScript

Sorting an Array containing Dictionaries with dates: A step-by-step guide

What is the best way to interact with all the rendered DOM elements in React that were created using the map method

I would like for this message to appear periodically following the initial execution

Guide to switching content within a DIV when the up and down buttons are pressed using JavaScript and jQuery

Unexpected server failure due to a new error occurring in the asynchronous authentication login function

Obtain information using AJAX calls with jQuery Flot