What is the relationship between Node.js and V8? Can Node work without V8?
V8 is a javascript engine which is used to build Node.js for server side rendering. V8 serves as an engine inside the Node.js environment which exposes it's API that can be interpretted too by addition of C++ code as it's open source. Node.js cannot run without V8 engine which is a JIT interpretor, Just in time, that interpretes and compiles the code into an optimized machine code in two steps. Without the Javascript interprettor, Node.js cannot run as it depends on the interface between C++ and javascript.
How come when you declare a global variable in any Node.js file it’s not really global to all modules?
A global variable is wrapped implicitely and hence is local to IIFE (An IIFE (Immediately Invoked Function Expression) is a function that runs the moment it is invoked or called in the JavaScript event loop) and prevents global var pollution.
When exporting the API of a Node module, why can we sometimes use exports and other times we have to use module.exports?
When we want to export multiple vars/classes/functions from one module to another we use exports. While, module.exports is used to import single entity from one module to another.
Can we require local files without using relative paths?
No, we cannot. But to avoid the long relative path we can use npm link to bring the smaller package in with the global modules which are found in node_modules folder.
Can different versions of the same package be used in the same application?
Yes, we can install new version of a package in isolation to prevent a big migration step when not required using aliases.
npm install <package_name_alias>@npm:<package_name>
What is the Event Loop? Is it part of V8?
A browser contains different applications/dependencies/libraries and hence an event loop of it's own that takes account of call stack which overrides and is different from the event loop of V8.
What is the Call Stack? Is it part of V8?
V8 is a JavaScript engine that provides a runtime environment. The JavaScript runtime environment, provided by V8 or any other JavaScript Engine consists of the memory heap, and call stack, where the actual JS code is being compiled and executed
What is the difference between setImmediate and process.nextTick?
setImmediate allows us to directly add a callback to the event queue. If you are familiar with the event loop, this executes the callback function after check phase. While, process.nextTick queues the callback function to get executed immediately after the current phase is executed. We should prefer setImmediate as process.nextTick can cause I/O starvation in recursive call.
How do you make an asynchronous function return a value?
We can wrap the async function call in an await function.
Can callbacks be used with promises or is it one way or the other?
With promises, you attach callbacks on the returned promise object. A callback is a function that is to be executed after another function has finished executing. Async callbacks are functions that are passed as arguments. and when that function is called it will start executing code in the background. Calling an async function will always return a Promise.
const getData = (dataEndpoint) => {
return new Promise ((resolve, reject) => {
//some request to the endpoint;
if(request is successful){
//do something;
resolve();
}
else if(there is an error){
reject();
}
});
};What are the major differences between spawn, exec, and fork?
Fork starts a new process which is a copy of the one that calls it, while exec replaces the current process image with another (different) one. Spawn creates new nodes for the children processes to run on all of which return data to the parent, while fork executes child processes on the same node as parent.
How does the cluster module work? How is it different than using a load balancer?
Load balancing distributes the workload amongst multiple servers to improve the performances meanwhile clustering, provides a way of creating child processes that runs simultaneously and share the same server port.
What are the --harmony-* flags?
allows you to use ECMAScript 6 (ES6) features that are marked as staged. A staged feature is a completed feature that's not yet considered stable and may have breaking changes when it reaches the shipping status.
How can you read and inspect the memory usage of a Node.js process?
We can use process.memoryUsage(), or go into chrome devtools->memory tab and heap snapshot option.
What will Node do when both the call stack and the event loop queue are empty?
It indicates there is no code (function) currently executing so Node will check the queue and will keep waiting for a process to execute some code for example if Node is being used as a http server it might be waiting for an API
What are V8 object and function templates?
A string template can be best used to suffice this: V8 Templates in Node.js are a feature that allows developers to embed expressions within a string using the ${expression} syntax. The expressions are evaluated at runtime and the resulting values are inserted into the string.
What is libuv and how does Node.js use it?
Libuv is a library written in the programming language C that helps nodejs to improve efficiency while running tasks parallelly. However, nodejs already have async API's. It uses Libuvs's thread pools if async API is not available in nodejs and processes are blocking the operations.
How can you make Node’s REPL always use JavaScript strict mode?
USe the command line option --use-strict
What is process.argv? What type of data does it hold?
process.argv is a property that holds an array of command-line values provided when the current process was initiated. The first element in the array is the absolute path to the Node, followed by the path to the file that’s running and finally any command-line arguments provided when the process was initiated.