## Submodule 7.2: Loops

• for loop
• while loop

### for loop

For loops are the most common looping in JavaScript. Typically, we use it when we know the number of iterations we need: a fixed number (count to ten) or the length of a data structure.

The for loop has the following syntax:

for (initial expression; test to run; increment) {    code block to be executed}
##### Example 1
/*let's count from 1 to 5*/for (var index = 1; index <= 5; index++){ console.log(index); }

In this example, we set our three expressions in the for loop.

• the initial expression: this is executed once before the loop runs, and typically sets the initial condition for the counter: in this case, setting index equal to 1
• the test to run before each iteration over the loop: if this evaluates to true, the loop will continue
• executed after each iteration through the loop. In this case, we use it to increment index to the next value.

Tip: Copy the above piece of code and paste it directly into the console, to see how it works.

##### Example 2

In this example, we create an array of colors and use the loop to iterate over the array and output its contents to the console.

/* remember that arrays start at zeroso we will loop from 0 to the length of the array*/var color = ["red", "green", "blue"];for (var i = 0; i < color.length; i++){  console.log(color[i]);}

Tip: Copy the above piece of code and paste it directly into the console, to see how it works.

for(var j = 0; j < 100; j++ ){  if (j % 2 == 1){       console.log(j)  };};