8 JavaScript Concepts to Learn for Tech Interviews

Preparing for tech interviews can be stressful, especially for new developers (and during a pandemic no less!). Luckily, there seems to be a repeating number of key concept questions that can be studied and committed to memory like we used to do with index cards in school as kids. To get you started, here are 8 common questions for JavaScript tech interviews that you can learn and start practicing today.


What is the difference between varconst and let?

Varconst and let are reserved words in JavaScript that allow you to declare and name variables. Before ES6, var was the only option to do this, with const and let being introduced in 2015.

Var allows you to declare a variable in any scope (global, function or block), is hoisted (explained more below) and initialized with an ‘undefined’ value, allowing that variable to be accessed without throwing an error at any point in the code. For this reason, you could also declare a variable with no value at all, and this would still be ok. With var, you can also reassign or redeclare the value of that variable.

examples of using var

Let is very similar to var, in the sense that it also allows you to reassign or redeclare the value at any point, and you can name a variable without a value. Unlike var, with let the variable is evaluated only at the time of execution, so we will get an error if the variable is referenced before it is written in the code. You also can’t declare a global variable using let.

examples using let

With const, a variable must always be initialized with a value, and that value can never change or be redeclared. If you try to do either, an error will immediately be thrown. Const can be used to declare a variable in any scope (including global), similar to var.

examples using const

#javascript #code-newbie #interview-questions #tech-interview #cheatsheet #programming

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8 JavaScript Concepts to Learn for Tech Interviews
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Sival Alethea

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Learn JavaScript - Full Course for Beginners. DO NOT MISS!!!

This complete 134-part JavaScript tutorial for beginners will teach you everything you need to know to get started with the JavaScript programming language.
⭐️Course Contents⭐️
0:00:00 Introduction
0:01:24 Running JavaScript
0:04:23 Comment Your Code
0:05:56 Declare Variables
0:06:15 Storing Values with the Assignment Operator
0:11:31 Initializing Variables with the Assignment Operator
0:11:58 Uninitialized Variables
0:12:40 Case Sensitivity in Variables
0:14:05 Add Two Numbers
0:14:34 Subtract One Number from Another
0:14:52 Multiply Two Numbers
0:15:12 Dividing Numbers
0:15:30 Increment
0:15:58 Decrement
0:16:22 Decimal Numbers
0:16:48 Multiply Two Decimals
0:17:18 Divide Decimals
0:17:33 Finding a Remainder
0:18:22 Augmented Addition
0:19:22 Augmented Subtraction
0:20:18 Augmented Multiplication
0:20:51 Augmented Division
0:21:19 Declare String Variables
0:22:01 Escaping Literal Quotes
0:23:44 Quoting Strings with Single Quotes
0:25:18 Escape Sequences
0:26:46 Plus Operator
0:27:49 Plus Equals Operator
0:29:01 Constructing Strings with Variables
0:30:14 Appending Variables to Strings
0:31:11 Length of a String
0:32:01 Bracket Notation
0:33:27 Understand String Immutability
0:34:23 Find the Nth Character
0:34:51 Find the Last Character
0:35:48 Find the Nth-to-Last Character
0:36:28 Word Blanks
0:40:44 Arrays
0:41:43 Nest Arrays
0:42:33 Access Array Data
0:43:34 Modify Array Data
0:44:48 Access Multi-Dimensional Arrays
0:46:30 push()
0:47:29 pop()
0:48:33 shift()
0:49:23 unshift()
0:50:36 Shopping List
0:51:41 Write Reusable with Functions
0:53:41 Arguments
0:55:43 Global Scope
0:59:31 Local Scope
1:00:46 Global vs Local Scope in Functions
1:02:40 Return a Value from a Function
1:03:55 Undefined Value returned
1:04:52 Assignment with a Returned Value
1:05:52 Stand in Line
1:08:41 Boolean Values
1:09:24 If Statements
1:11:51 Equality Operator
1:13:18 Strict Equality Operator
1:14:43 Comparing different values
1:15:38 Inequality Operator
1:16:20 Strict Inequality Operator
1:17:05 Greater Than Operator
1:17:39 Greater Than Or Equal To Operator
1:18:09 Less Than Operator
1:18:44 Less Than Or Equal To Operator
1:19:17 And Operator
1:20:41 Or Operator
1:21:37 Else Statements
1:22:27 Else If Statements
1:23:30 Logical Order in If Else Statements
1:24:45 Chaining If Else Statements
1:27:45 Golf Code
1:32:15 Switch Statements
1:35:46 Default Option in Switch Statements
1:37:23 Identical Options in Switch Statements
1:39:20 Replacing If Else Chains with Switch
1:41:11 Returning Boolean Values from Functions
1:42:20 Return Early Pattern for Functions
1:43:38 Counting Cards
1:49:11 Build Objects
1:50:46 Dot Notation
1:51:33 Bracket Notation
1:52:47 Variables
1:53:34 Updating Object Properties
1:54:30 Add New Properties to Object
1:55:19 Delete Properties from Object
1:55:54 Objects for Lookups
1:57:43 Testing Objects for Properties
1:59:15 Manipulating Complex Objects
2:01:00 Nested Objects
2:01:53 Nested Arrays
2:03:06 Record Collection
2:10:15 While Loops
2:11:35 For Loops
2:13:56 Odd Numbers With a For Loop
2:15:28 Count Backwards With a For Loop
2:17:08 Iterate Through an Array with a For Loop
2:19:43 Nesting For Loops
2:22:45 Do…While Loops
2:24:12 Profile Lookup
2:28:18 Random Fractions
2:28:54 Random Whole Numbers
2:30:21 Random Whole Numbers within a Range
2:31:46 parseInt Function
2:32:36 parseInt Function with a Radix
2:33:29 Ternary Operator
2:34:57 Multiple Ternary Operators
2:36:57 var vs let
2:39:02 var vs let scopes
2:41:32 const Keyword
2:43:40 Mutate an Array Declared with const
2:44:52 Prevent Object Mutation
2:47:17 Arrow Functions
2:28:24 Arrow Functions with Parameters
2:49:27 Higher Order Arrow Functions
2:53:04 Default Parameters
2:54:00 Rest Operator
2:55:31 Spread Operator
2:57:18 Destructuring Assignment: Objects
3:00:18 Destructuring Assignment: Nested Objects
3:01:55 Destructuring Assignment: Arrays
3:03:40 Destructuring Assignment with Rest Operator to Reassign Array
3:05:05 Destructuring Assignment to Pass an Object
3:06:39 Template Literals
3:10:43 Simple Fields
3:12:24 Declarative Functions
3:12:56 class Syntax
3:15:11 getters and setters
3:20:25 import vs require
3:22:33 export
3:23:40 * to Import
3:24:50 export default
3:25:26 Import a Default Export
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The origin of the article: https://www.youtube.com/watch?v=PkZNo7MFNFg&list=PLWKjhJtqVAblfum5WiQblKPwIbqYXkDoC&index=4

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8 JavaScript Concepts to Learn for Tech Interviews

Preparing for tech interviews can be stressful, especially for new developers (and during a pandemic no less!). Luckily, there seems to be a repeating number of key concept questions that can be studied and committed to memory like we used to do with index cards in school as kids. To get you started, here are 8 common questions for JavaScript tech interviews that you can learn and start practicing today.


What is the difference between varconst and let?

Varconst and let are reserved words in JavaScript that allow you to declare and name variables. Before ES6, var was the only option to do this, with const and let being introduced in 2015.

Var allows you to declare a variable in any scope (global, function or block), is hoisted (explained more below) and initialized with an ‘undefined’ value, allowing that variable to be accessed without throwing an error at any point in the code. For this reason, you could also declare a variable with no value at all, and this would still be ok. With var, you can also reassign or redeclare the value of that variable.

examples of using var

Let is very similar to var, in the sense that it also allows you to reassign or redeclare the value at any point, and you can name a variable without a value. Unlike var, with let the variable is evaluated only at the time of execution, so we will get an error if the variable is referenced before it is written in the code. You also can’t declare a global variable using let.

examples using let

With const, a variable must always be initialized with a value, and that value can never change or be redeclared. If you try to do either, an error will immediately be thrown. Const can be used to declare a variable in any scope (including global), similar to var.

examples using const

#javascript #code-newbie #interview-questions #tech-interview #cheatsheet #programming

Learning JavaScript: Working with Strings

Strings are the second most common data type used in JavaScript, and in many cases, since JavaScript is so widely used for web applications, it is the prominent data type. In this article I’ll discuss how strings work in JavaScript and how to work with them efficiently and effectively. I’ll also discuss some newer abilities of strings that are just being discovered and used.

Strings Defined

A string is any set of 0 or more characters enclosed in either single quotes or double quotes. The characters in a string can be alphabetic characters, numbers, symbols, and spaces. Here are some examples of JavaScript string literals:

"hello world"
'good bye, world!'
"1600 Pennsylvania Avenue"
'$*&!@ it!'

If you are using single quotes in your string, and you need to embed a single quote to write out a contraction, you use the backslash character (\) as an escape character. To see why you need to do this, let’s look at what happens when you don’t escape a single quote by writing out such a string in the JavaScript shell:

js> 'can't'
typein:1:5 SyntaxError: unexpected token: identifier:
typein:1:5 'can't'
typein:1:5 .....^

The interpreter can’t figure out what to do with the ‘t’ after the single quote.

Now watch what happens when we escape the single quote:

js> 'can\'t'
"can't"

The escape character tells the interpreter to treat the single quote as an apostrophe and not as an “end-of-string” character.

You can embed other characters into a string, including the newline character (\n) and the tab character (\t). Here are some examples using the shell:

js> print("Hello, \n world!");
Hello,
world!
js> print("Hello, \tworld");
Hello,  world

#javascript-training #learn-to-code #learn-to-program #javascript #javascript-tutorial #deep learning

Niraj Kafle

1589255577

The essential JavaScript concepts that you should understand

As a JavaScript developer of any level, you need to understand its foundational concepts and some of the new ideas that help us developing code. In this article, we are going to review 16 basic concepts. So without further ado, let’s get to it.

#javascript-interview #javascript-development #javascript-fundamental #javascript #javascript-tips

Learning JavaScript: Computing with Object Methods

JavaScript has a set of built-in methods you can use with your user-defined objects. In this article I’m going to discuss several of these methods and how you can use them in your JavaScript programs.

Object.assign

The Object.assign method is used to make a copy of one object into another object. The syntax template for this method is:

Object.assign(target, source);

where source is the object you are copying from and target is the object you are copying into. This method returns the target object if you want to assign it.

Here is a sample program that demonstrates how to use Object.assign:

function Student(name, id, grades) {
  this.name = name;
  this.id = id;
  this.grades = grades;
}
let st1 = new Student("",0,[]);
et st2 = new Student("Jane Doe", 123, [91, 92, 93]);
Object.assign(st1, st2);
print(`${st1.name}, ${st1.id}\n[${st1.grades}]`);

The output from this program is:

Jane Doe, 123
[91, 92, 93]

A good reason to use this method is to make sure that a new object has all the properties and values of the old object. You may accidentally leave something out when writing your own method, while Object.assign will systematically make sure all properties and values are assigned to the new object.

Object.create

The Object.create method creates a new object from an existing object prototype. Here is the syntax template for this method:

const|let|var object-name = Object.create(existing-object);

Let’s look at a few examples to see how this method works in practice. The first example creates a new object from a function and then creates a second object using Object.create:

function Student(name, id, grades) {
  this.name = name;
  this.id = id;
  this.grades = grades;
}
let st1 = new Student("Bob Green", 1234, [81, 77, 92]);
print(`${st1.name}, ${st1.id}\n${st1.grades}`);
let st2 = Object.create(st1);
print(`${st2.name}, ${st2.id}\n${st2.grades}`);

The output from this program is:

Bob Green, 1234
81,77,92
Bob Green, 1234
81,77,92

Code must be written to change the properties of the newly created object.

#learn-to-code #javascript-development #learn-to-program #javascript #learning-javascript