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
Sival Alethea

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
📺 The video in this post was made by freeCodeCamp.org
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

Tia  Gottlieb

Tia Gottlieb

1596632340

Learning JavaScript: Statements, Arithmetic, and Math

In this article I will discuss how to perform arithmetic and more advanced mathematical operations in JavaScript. First, though, I need to discuss how statements are formed and used in JavaScript.

Statements

JavaScript programs are made up of statements. A statement can be anything from a single function call or command to even just a variable name. JavaScript evaluates statements and then executes them.

For example, when you create a variable, you write a statement:

let number = 100;

JavaScript recognizes this as a statement and evaluates it by following its grammar rules. In this case the rule is to assign the expression on the right-hand sign of the assignment operator to the variable on the left-hand side.

As I mentioned above, a statement can be just an expression, as in the following example:

js> 1;
1

You can do the same thing with a variable:

js> let name = "Brendan";
js> name
"Brendan"

Statements can be much more complicated than these examples, though, as you’ll learn as you get deeper into JavaScript. So far, you have seen examples of two types of statements — variable declaration and assignment statements and print statements.

JavaScript Arithmetic

Arithmetic is performed in JavaScript using the arithmetic operators. There are five arithmetic operators:

  • + (Addition)
  • - (Subtraction)
  • * (Multiplication)
  • / (Division)
  • % (Modulo/Remainder)

These operators are binary operators, meaning there must be values on either side of the operator. The + operator and the -operator can also be used as unary operators, in which can they are used to distinguish the sign (positive or negative) of a number.

The JavaScript arithmetic operators also have an order of operations, or precedence, they follow when used in a statement. The order of operations is: 1) modulo; 2) multiplication and division; 3) addition and subtraction.

You can use parentheses to modify the order of operations. When an arithmetic expression is placed inside parentheses, that expression is evaluated before any other operations.

For example, take the expression:

let n = 100 + 3 * 22;

Does n get the value 2266, 103 * 26, or does the variable get the value 166? Without parentheses the value of n is 166 because the multiplication takes place before the addition due to the precedence of the multiplication operator over the addition operator.

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