Javascript.md

JavaScript Notes:

Mutability

Javascript have 7 premitive data types, (string, number, bigint, bool, undefined, null, & symbol), these are immutable, We cannot change it's value, we only can reassign. Eexample bellow.

let text = 'abcde'
text[1] = 'z'
console.log(text) //ans: abcde

N.B Other types like object, function are mutable, theire value can be changed. Example for Object (Array)

const arr = [1,2,3]
arr.length = 0
console.log(arr) //arr of 0 length

Accidental Global Variable

(()=>{
 let a = b = 0;
 console.log(a, b); //a=0. b=0;
})();
console.log(a); // a isn't defined
console.log(b); // 0

The above program works as only a is let scoped variable, b is like window.b, not with let scoped. This is called Accidental Global Variable

Coercion

if 2 operands are connected with + operand, both operands will be changed to a string first with toString() method and then concatenated. The other operator such as - , *, or / will change the operand to a number. If it cannot be coerced to a number, NaN will be returned.

console.log(1 +  +"2" + "3"); //ans: 33
console.log(1 +  -"1" + "3"); //ans: 03
console.log(+"1" +  "1" + "3"); //ans: 113
console.log( "A" - "B" + "2"); //ans: NaN2

Sort

const a = [1,5,2,10,3];
console.log(a.sort()); //[1,10,2,3,5];

if we ommitted the comparison function from sort(), the array elements are converted to strings, then sorted according to each character’s Unicode code point value.