What is the name and what is the omission operator for;

For example, in the code below I use ; instead of leaving, var or const. What is the name of this operator?

var cars = ["Audi", "BMW", "Corolla", "Honda"]
let i = 2;
let len = cars.length;
let text = "";
for (; i < len; i++) {
    text += cars[i] + "<br>";
}

Does it serve to clone other variables?

Answer

Normal for loops have 3 components inside the brackets, all of which are optional and you can have any combination of them:

for ([initialExpression]; [conditionExpression]; [incrementExpression])
    statement

The semicolon ; is not an omission operator as much as it is a separator for the 3 components. If you omit any component, the separating semicolon stays, otherwise it would be ambiguous which component was omitted.

Your example omitted the initialization statement component. This is not an operator, does not have an established name, and it does nothing (i.e. avoids defining a variable exclusively for the loop as is typically the case).

As Nick mentioned, omitting components in for loops is often bad practice and should be avoided. But it can be fine in some situations like when re-using a variable across multiple for loops.

Relevant Resource: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration#for_statement