There are a couple of different kinds of loop structures in JavaScript, but a 'for loop' is by far the most popular

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For Loops have 4 parts: example for loop

 for (let i=0; i<10; i=i+){

  //do something

}

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FIRST we initialize a variable to keep track of the number = lets call this a counter variable

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let i=0;

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Inside loops we tend to use short variable names such as i or j if they are just controlling the 'flow' of the loop.

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SECOND we define the test condition for the loop, this gets evaluated (tested ) each time the loop is about to start. Our example we are testing if our counter variable is smallet than 10

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i < 10;

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THIRD we are (defining a way ) updating the counter variable that then gets evaluated at the end of the loop. We are getting the current value of the variable i and adding 1 to it.

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i = i + 1; 

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FORTH, final part, is inside the { } we write the code that the we want repeated. Once the variable counter doesn't 'satisfy' the test i<10 the loop terminates.

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*/

function setup() {

        createCanvas(800, 300);

}

function draw() {

        background(1, 75, 100);

        // circle properties

        fill(237, 34, 93);

        noStroke();

        let diameter = 40;

        for (let i=0; i<width/diameter; i=i+1) {

                for (let j=0; j<height/diameter; j=j+1) {

                        ellipse(

                                diameter/2 + i * diameter,

                                diameter/2 + j * diameter,

                                diameter * random(), // using the random function

                                diameter

                        );

                }

        }

}

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