JavaScript
- Getting started with JavaScript
- Awesome Book
- Awesome Community
- Awesome Course
- Awesome Tutorial
- Awesome YouTube
- .postMessage() and MessageEvent
- AJAX
- Anti-patterns
- Arithmetic (Math)
- Arrays
- Arrow Functions
- Async functions (async/await)
- Async Iterators
- Automatic Semicolon Insertion - ASI
- Battery Status API
- Behavioral Design Patterns
- Binary Data
- Bitwise operators
- Bitwise Operators - Real World Examples (snippets)
- BOM (Browser Object Model)
- Built-in Constants
- Callbacks
- Classes
- Comments
- Comparison Operations
- Conditions
- Console
- Constructor functions
- Context (this)
- Cookies
- Creational Design Patterns
- Custom Elements
- Data attributes
- Data Manipulation
- Datatypes in Javascript
- Date
- Date Comparison
- Debugging
- Declarations and Assignments
- Destructuring assignment
- Detecting browser
- Enumerations
- Error Handling
- Escape Sequences
- Evaluating JavaScript
- Events
- execCommand and contenteditable
- Fetch
- File API, Blobs and FileReaders
- Fluent API
- Functional JavaScript
- Functions
- Generators
- Geolocation
- Global error handling in browsers
- History
- How to make iterator usable inside async callback function
- IndexedDB
- Inheritance
- Intervals and Timeouts
- JavaScript Variables
- JSON
- Linters - Ensuring code quality
- Localization
- Loops
- Map
- Memory efficiency
- Method Chaining
- Modals - Prompts
- Modularization Techniques
- Modules
- Namespacing
- Navigator Object
- Notifications API
- Objects
- Performance Tips
- Promises
- Prototypes, objects
- Proxy
- Regular expressions
- requestAnimationFrame
- Reserved Keywords
- Same Origin Policy & Cross-Origin Communication
- Scope
- Screen
- Security issues
- Selection API
- Server-sent events
- Set
- Setters and Getters
- Strict mode
- Strings
- Symbols
- Tail Call Optimization
- Template Literals
- The Event Loop
- Tilde ~
- Timestamps
- Transpiling
- Unary Operators
- Unit Testing Javascript
- Using javascript to get/set CSS custom variables
- Variable coercion/conversion
- Vibration API
- WeakMap
- Creating a WeakMap object
- Assigning a value to the key
- Checking if an element with the key exists
- Getting a value associated to the key
- Removing an element with the key
- Weak reference demo
- WeakSet
- Web Cryptography API
- Web Storage
- WebSockets
- Workers
JavaScript WeakMap Checking if an element with the key exists
Example
To check if an element with a specified key exits in a WeakMap, use the .has() method. It returns true if it exits, and otherwise false.
const obj1 = {},
obj2 = {};
const weakmap = new WeakMap([[obj1, 7]]);
console.log(weakmap.has(obj1)); // true
console.log(weakmap.has(obj2)); // false
