Q331. How to loop inside JSX?
You can simply use `Array.prototype.map` with ES6 _arrow function_ syntax. For example, the `items` array of objects is mapped into an array of components: ```jsx harmony...
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Q332. Why do we need callbacks?
The callbacks are needed because javascript is an event driven language. That means instead of waiting for a response, javascript will keep executing while listening for ...
Q333. How do you access props in attribute quotes?
React (or JSX) doesn't support variable interpolation inside an attribute value. The below representation won't work: ```jsx harmony ``` But you can put any JS expression...
Q334. Row comparison operators with subqueries?
`IN`, `ANY`, `ALL`, `EXISTS`, `NOT EXISTS`, and standard comparison operators (`=`, `>`, `=`, ` ALL (SELECT salary FROM employees WHERE dept = 'Sales') WHERE salary > ANY...
Q335. What is CSS?
CSS stands for Cascading Style Sheets. CSS is used to define styles for web pages, including the design, layout and variations in display for different devices and screen...
Q336. What is a callback hell?
Callback Hell is an anti-pattern with multiple nested callbacks which makes code hard to read and debug when dealing with asynchronous logic. The callback hell looks like...
Q337. What is React proptype array with shape?
If you want to pass an array of objects to a component with a particular shape then use `React.PropTypes.shape()` as an argument to `React.PropTypes.arrayOf()`. ```javasc...
Q338. What are server-sent events?
Server-sent events (SSE) is a server push technology enabling a browser to receive automatic updates from a server via HTTP connection without resorting to polling. These...
Q339. How to conditionally apply class attributes?
You shouldn't use curly braces inside quotes because it is going to be evaluated as a string. ```jsx harmony ``` Instead you need to move curly braces outside (don't forg...
Q340. How do you receive server-sent event notifications?
The EventSource object is used to receive server-sent event notifications. For example, you can receive messages from server as below, ```javascript if (typeof EventSourc...