Day 6 - JavaScript Fundamentals

15 January, 2024

Contributors

Keshav K

@kesava-karri

Day 6 - JavaScript Fundamentals
- Add JavaScript to html
- - Similar to adding external css to a html page, we can add using <script src="script.js"> element to add external js to the html page.
  - or writing all the javascript code with in the opening & closing tags of <script>
  - To add external css we use <link> element within the <head> element in html where as the <script> is added to the <body> element since only metadata stays in the <head> of the html file.
- 8 Data types in JavaScript - mdn docs, javascript.info link
- - Number
  - BigInt
  - String
  - Boolean
  - null
  - - In JavaScript, null is not a “reference to a non-existing object” or a “null pointer” like in some other languages.
    - It’s just a special value which represents “nothing”, “empty” or “value unknown”.
  - undefined
  - Symbol
  - Object
  - Object is the only reference type and the rest are considered primitive data types.
- All operators in JavaScript including the assignment operator (=) returns a value 🙂.
- - Example
```
let a = 1;
let b = 2;

let c = 3 - (a = b + 1);

alert( a ); // 3
alert( c ); // 0
```
- Escape characters - https://developer.mozilla.org/en-US/docs/Learn/JavaScript/First_steps/Strings#including_quotes_in_strings:~:text=Escaping characters means
- - For the single or double quotes to be considered within another string we use a \\ right before those quotes or other special characters - This is to escape that character.
```
const bigmouth = 'I\\'ve got no right to take my place…';
console.log(bigmouth);
// output: I've got no right to take my place…
```
- + is also used for concatenating the strings
- - since + is a binary operator & javascript goes from left to right for evaluating, it converts it to string if a either of the operand is a string else converts to num
  - Example
```
console.log(1 + "2" + 3);

// output: 123

console.log(2 + 3 + "8");

// output: 58
```
- All non-numbers are tried to be converted to numbers when arithmetic operations are done in js, with some exceptions to +
- - Example
```
console.log(2 + 3 - "8");

// output: -3
```
- Declaration in js returns undefined
- - let a; → returns undefined
  - Also when a declaration combined with assignment would also return undefined
- undefined and null have a weird relation
- - the non-strict comparison (==) returns true
  - and the strict comparison (===) since checks the type returns false
  - null is never equal to anything except as mentioned above

Day 6 - JavaScript Fundamentals

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