Code-Snippet.txt

1) Remove an item from the Array

const array = [2, 5, 9];

console.log(array); // [2, 5, 9]

const index = array.indexOf(5);
if (index > -1) {
  array.splice(index, 1);
}

console.log(array); // [2, 9]

2) 

Scenario 1: [NO STRICT MODE]

var city = "Chicago"
console.log(city) // Prints the city name, i.e. Chicago
Scenario 2: [NO STRICT MODE]

city = "Chicago"
console.log(city) // Prints the city name, i.e. Chicago

Scenario 3: [STRICT MODE]

'use strict';

city = "Chicago"
console.log(city) // Reference Error: asignment is undeclared variable city.


3) A closure is a pairing of:

A function, and
A reference to that function's outer scope (lexical environment)
A lexical environment is part of every execution context (stack frame) and is a map between identifiers (ie. local variable names) and values.

Every function in JavaScript maintains a reference to its outer lexical environment. This reference is used to configure the execution context created when a function is invoked. This reference enables code inside the function to "see" variables declared outside the function, regardless of when and where the function is called.

If a function was called by a function, which in turn was called by another function, then a chain of references to outer lexical environments is created. This chain is called the scope chain.

In the following code, inner forms a closure with the lexical environment of the execution context created when foo is invoked, closing over variable secret:


function foo() {
  const secret = Math.trunc(Math.random()*100)
  return function inner() {
    console.log(`The secret number is ${secret}.`)
  }
}
const f = foo() // `secret` is not directly accessible from outside `foo`
f() // The only way to retrieve `secret`, is to invoke `f`


4) To check whether a string contains a substring:

const string = "foo";
const substring = "oo";

console.log(string.includes(substring)); // true


5) 

const sentence = 'The quick brown fox jumps over the lazy dog.';

const word = 'fox';

console.log(`The word "${word}" ${sentence.includes(word) ? 'is' : 'is not'} in the sentence`); // "The word "fox" is in the sentence"


6) Remove a property from a JavaScript object:

delete myObject.regex;
// or,
delete myObject['regex'];
// or,
var prop = "regex";
delete myObject[prop];
----------------------

ar myObject = {
    "ircEvent": "PRIVMSG",
    "method": "newURI",
    "regex": "^http://.*"
};
delete myObject.regex;

console.log(myObject); // {"ircEvent": "PRIVMSG",  "method": "newURI"}

7) 

'' == '0'           // false
0 == ''             // true
0 == '0'            // true

false == 'false'    // false
false == '0'        // true

false == undefined  // false
false == null       // false
null == undefined   // true

' \t\r\n ' == 0     // true

== operator just compares the values not datatype.

=== operator compare the values with comparison of its datatype.

Example :

1 == "1" //true

1 === "1" //false


8) "let" and "var" difference :

function run() {
  var foo = "Foo";
  let bar = "Bar";

  console.log(foo, bar); // Foo Bar

  {
    var moo = "Mooo"
    let baz = "Bazz";
    console.log(moo, baz); // Mooo Bazz
  }

  console.log(moo); // Mooo
  console.log(baz); // ReferenceError
}

run();

------------------------------------

function run() {
  console.log(foo); // undefined
  var foo = "Foo";
  console.log(foo); // Foo
}

run();function checkHoisting() {
  console.log(foo); // ReferenceError
  let foo = "Foo";
  console.log(foo); // Foo
}

checkHoisting();

---------------------------------------

function checkHoisting() {
  console.log(foo); // ReferenceError
  let foo = "Foo";
  console.log(foo); // Foo
}

checkHoisting();

9) 

var a = ["a", "b", "c"];
a.forEach(function(entry) {
    console.log(entry); // a b c
});


10) Check whether "Checkbox" is checked or not:

$("#isAgeSelected").on('change', function() {
  if ($("#isAgeSelected").is(':checked'))
    alert("checked");
  else {
    alert("unchecked");
  }
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="isAgeSelected" />
<div id="txtAge" style="display:none">
  Age is selected
</div>