For loop with no condition - Javascript

Current starts at 20.

let current = 20

It is incremented by 1

current = current + 1

Once it is divisible by 7 (0 means no remainder so it is divisible)

  if (current % 7 == 0)

Print current(21) -> 21 % 7 = 0 and stop

console.log(current);
break;

First you have to know what the % sign means.

% is used for modulus - It means remainder.

For Example:-

5%2 --- // (5/2) here remainder is 1 so result is 1.

Now move to the actual question:--

LOOP

for (let current = 20; ; current = current + 1) {
  if (current % 7 == 0) {
    console.log(current);
    break;
 }
}

In first Turn

1) current value is 20

2) if(current % 7 == 0) -- Define Condition, the value of remainder when "current" is divided by 7 (current/7) Here this will resolve as

a) (20%7 = 6 (remainder))

b) if(6 == 0) -- false

3) Skip the if block

4) Now, current = current+1 // current = 21

In Second Turn

1) current value is 21

2) if(current % 7 == 0)

Resolve as ---

 a) (21%7 = 0 (remainder))

 b) if(0  == 0) -- true

3) Goes into if block

4) Print the value of current on console, i.e., 21

5) execute break statement and terminate the loop

--- End Program ---

The empty statement (i.e. just a semi colon) is a valid statement in javascript. This just means that there is no condition being checked at the beginning of each loop iteration in that for loop.

Now, if we look at what this loop does, we can see that on the first iteration, current = 20 and hence the inner condition fails (since 20 is not divisible by 7).

The next iteration occurs, current is incremented to 21, and now the inner condition passes (21 is divisible by 7). Hence, we print 21 and break out of the loop.

The three parts within for parentheses are:

• What to do before the loop
• A predicate, if it returns true, continue looping
• What to do after each turn through the loop

So:

for(a;b;c) {
   d
}

... is equivalent to:

a;
while(b) {
  d;
  c;
}

... with the bonus feature, that if any of a,b,c,d are missing, it "works" b being missing is equivalent to true.

So:

int i=0;
for(;i<10;i++) {
   println('hello');
}`

... is equivalent to:

int i=0;
while(i<10) {
   println('hello'); 
   i++;
}

And:

for(int i=0;;i++) {
   println('hello');
}`

... is equivalent to:

int i=0;
while(true) {
   println('hello'); 
   i++;
}

... which is an infinite loop because while(true).

And:

for(int i=0;i<10;) {
   println('hello');
}`

... is equivalent to:

int i=0;
while(i<10) {
   println('hello'); 
}

(... which is an infinite loop because i never reaches 10)

And:

for(;;) { println('hello'); }

is:

while(true) { println('hello'); }