JavaScript exercises

Check for type

var a = []

if (abc instanceof Array){

 console.log('true')
 
}

=> true
______________________________

var a = []

if (abc instanceof Number){ 

  console.log('true') 
  
    }else{ 
  
  console.log('false')
  
}
  
=> false  

Functions

function test(a,b) {
    
  console.log("sum of", a, " and ", b, " is equal to ", a + b)
  
}

test(20,40);

=> sum of 20  and  40  is equal to  60

________________________________

function testFunc(b,c) {     // or var testFunction = function(b,c)                             
    
    var sum = 0;
    
    for(var i = 0; i < arguments.length; i ++) {
        
        sum = sum + arguments[i];
        
    }
    
    console.log('sum of ', b, ' and ', c, ' is equal to ', sum)

}

testFunc(40,4)

=> sum of  40  and  4  is equal to  44

_______________________________

var arrayOfNumbers = [1,2,3,5,27,88,3,23];

function greaterThan(sourse, value) {
    
    var result = [];
    
    for (var i = 0; i < sourse.length; i++){
    
        if (sourse[i] > value ) {
    
            result.push(sourse[i]);
    
        }
    
    }
    
    return result;

}


console.log(greaterThan4(arrayOfNumbers, 4));

=> [5, 27, 88, 23]

_______________________________

var arrayOfNumbers = [1,2,3,5,27,88,3,23];

function filter(sourse, filterFn) {
    
    var result = [];
    
    for (var i = 0; i < sourse.length; i++){
    
        if (filterFn(sourse[i])) {
    
            result.push(sourse[i]);
    
        }
    
    }
    
    return result;

}


console.log(greaterThan4(arrayOfNumbers, 4));

=> [5, 27, 88, 23]

function greaterThan4(value){
    return value > 4;
}

console.log(filter(arrayOfNumbers,greaterThan4));

=> [5, 27, 88, 23]

______________________________
var a = 1;

function f1(b){
    var c = 10;
    
    return a + b + c;
}

console.log(f1(2));

=> 13

Iterations

var a = [1, '3', true, 3.4]

for (var i = 0; i < a.length; i++) {
  
  console.log(i, a[i]); 

}

=>
0 1
1 "3"
2 true
3 "add"

More functions

var s = 'Hi';
console.log(s.concat(' Anna')); /* or console.log(s + " Anna") */

=> Hi Anna
______________________________________

var s = 'Hello there';
console.log(s.indexOf('there'));

=> 6 /*6th position; if there it doesn't find anything it returns -1*/

var s = 'Hello there';
if (s.indexOf('sdjskjd') == -1 ) {
  console.log('position not found');
} else {
  console.log('position found');
}
_________________________

var s = 'Hello there';

var i = s.indexOf('e');

if (i == -1 ) {
  console.log('position not found');
} else {
  console.log('position found');
}

=> position found
_________________________

var s = '1|2|3|4|5|';
var matched = s.match(/\d\|/);*
console.log(matched);

=> ["1|", index: 0, input: "1|2|3|4|5|"]

* or  s.match(/\d\|/9); then result is ["1|", "2|", "3|", "4|", "5|"]

list of methods for strings:

replace()
slice()
split()
trim()
toLowerCase()
toUpperCase()

_____________________________________

var s = 'car, box, move, place';
console.log(s.split(','));

=> ["car", " box", " move", " place"]
_____________________________________

var s = 'car, box, move, place';
console.log(s.split(','));

for(var i = 0; i < s.length; i++) {
  console.log(s[i].trim());
}

=> 
["car", " box", " move", " place"]
 c
 a
 r
 ,
 
b
o
x
,
 
m
o
v
e
,
 
p
l
a
c
e

Objects

// create new object

var s = new String ('objectsstring');

=> s
String {0: "o", 1: "b", 2: "j", 3: "e", 4: "c", 5: "t", 6: "s", 7: "s", 8: "t", 9: "r", 10: "i", 11: "n", 12: "g", length: 13, [[PrimitiveValue]]: "objectsstring"}