Can you figure out the value of r? How does it relate to Boolean operators and objects?
var data = {x:123, y:456};
var r = data && data.x || 0;
Update:
Upon running the code snippet, I noticed that r consistently equals x. However, the reason behind this outcome remained unclear to me.
Consider the task at hand and refer to JavaScript Operator Precedence
var r = data && data.x || 0
The && operator takes precedence over the || operator. It returns the last operand if both are true, otherwise it returns false. Therefore, the expression simplifies to:
var r = data.x || 0
Now, the || operator will return the first truthy operand, in this case, data.x:
var r = data.x
When it comes to Javascript objects themselves, they always evaluate to true, even if empty (e.g., obj = {})
However, when validating an object's property, things change: if the property has a Boolean value of false or a numeric value of 0, it will be considered false because 0 == false but 0 !== false.
For example:
var data = { x:false, y:456 };
var r = data && data.x || 999;r would be 999, just like if data.x was set to `0.
According to information from the Mozilla Developer Network (MDN),
Javascript utilizes type coercion in situations involving Booleans.
Within Javascript, there exist 8 values considered "falsy"
In the provided example, data && data.x || 0, the use of && and || signifies Boolean context. The variable data is coerced as a Boolean. Should it not match any of the aforementioned values, it will be coerced into true.
Many developers often verify if an object is defined by checking whether it is "falsy" or not (i.e. neither null nor undefined). The given example could be rephrased as
var r = 0;
if(data && data.x){
r = data.x;
}
This approach explicitly conveys that you are confirming the existence of data and ensuring that data.x is not falsy (such as 0). It is a common practice used to prevent null reference errors when uncertain about the validity of a variable containing an object.
I am currently in the process of developing a custom build using core-js. Following the instructions provided, I initiated the following commands: npm i core-js && cd node_modules/core-js && npm i The process seemed to go smoothly. Then, ...
In my HTML, I have a snippet of code that defines a custom <SelectField> component using a <select> tag like this: export default function SelectField(props) { /* PARAMETERS: - fieldname (String) - fieldID (String) - options (A ...
I am in the process of creating a custom directive that will ensure only one element is active at a time. Directive: displayOneAtATime Description: This directive can be applied to a DOM node to guarantee that only one element with this directive can be v ...
As a novice, I find it challenging to interpret documentation, but I can grasp the code's meaning once I see it in action. Take app.use([path,] callback [, callback...]), for example. I know how to utilize this method, yet I still struggle with unde ...
I'm feeling a bit lost as I navigate my way through Angular. As a newcomer, I find myself writing quite a bit of code to keep track of the logged-in state. However, this approach seems fragile and unreliable. Currently, I rely on a global variable to ...
I'm attempting to retrieve the top and bottom measurements from multiple elements using the IntersectionObserver. However, once I have the measurements, I'm unsure how to stop observing the elements. The issue is that each element has a position ...
I am currently working on building a nested parent-child system where the child schema mirrors that of the parent. Below is the schema for the parent, where children refer back to the parentSchema: var mongoose = require("mongoose"); var parentSchema ...
Currently, I am in the process of developing a todo-list application that includes fields for description, priority, and date. To capture the priority and description inputs, I utilize TextFields which trigger the {inputChanged} function. Within this funct ...
I am having trouble using preventdefault to stop an action. I'm sorry if the solution is obvious, but I can't seem to locate the mistake. Why isn't it preventing the link from being followed? Here is a link to my jsfiddle: http://jsfiddle.ne ...
As I dive into Next JS, I've hit my first roadblock. Currently, I am working on a page that showcases various podcast episodes with preview cards on the homepage. The card component code looks like this: import React from 'react'; import Li ...
As a hobbyist coder, I'm facing a challenging problem with building a dynamic HTML/CSS calendar. My goal is to have cells filled in based on today's date. However, when I attempt to add days to fill in another 13 days by looping through HTML elem ...
I developed a To-Do List using Javascript, HTML, and IndexedDB to store the items in the database so that they won't be deleted when the browser is refreshed. I also want to include the date for each item, however, whenever I add an item, the date end ...
I am currently working on a TypeScript-based React application. To start off, I used the following command to create my React app with TypeScript template: npx create-react-app test-app --template typescript It's worth noting that eslint comes pre-co ...
I'm in the process of developing an application using Next.js along with redux by utilizing this particular example. Below is a snippet from my store.js: // REDUCERS const authReducer = (state = null, action) => { switch (action.type){ ...
Is there a method to maintain a reference of the same collection while altering the ordering using firestore? TLDR: I am looking to achieve similar functionality as demonstrated in: , but since my data is sourced from firestore, I am struggling to find th ...
I am working with an object called "config" and an id named "id". My goal is to create an array of objects structured like this: [ "id" : { "config1: ... "config2: ... "config3: ... } "id2" : { "config ...
My node.js application/module is currently functioning well with a plug-in concept. This means that my module acts like a proxy with additional capabilities, such as adding new functionality to the existing methods. To achieve this, follow these steps: Cl ...
I am working on a complex data-driven application that heavily relies on Ajax and Javascript. As the amount of data returned for certain value selections increases, the application is starting to struggle. This is more of a brainstorming session than a q ...
Is there a way to restrict the placement of markers on a map? I am looking for a solution that allows me to limit the marker position within a specific area, such as a town, with a radius of 10km. It should prevent users from dragging or creating new mark ...
Within the realm of Angular, I am dealing with interfaces that take on a structure similar to this (please note that this code is not my own): export interface Vehicles { id: number; cars: Car; trucks: Truck; } Export interface Car { make: ...