for

The for statement creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement (usually a block statement) to be executed in the loop.

let str = '';

for (let i = 0; i < 9; i++) {
  str = str + i;
}

for…of

The for...of statement executes a loop that operates on a sequence of values sourced from an iterable object.

Iterable objects include instances of built-ins such as Array, String, TypedArray, Map, Set, NodeList (and other DOM collections), as well as the arguments object, generators produced by generator functions, and user-defined iterables.

When a for...of loop iterates over an iterable, it first calls the iterable’s [@@iterator]() method, which returns an iterator, and then repeatedly calls the resulting iterator’s next() method to produce the sequence of values to be assigned to variable.

const array1 = ['a', 'b', 'c'];
for (const element of array1) {
  console.log(element);
}
// Expected output: "a"
// Expected output: "b"
// Expected output: "c"

for…in

The for...in statement iterates over all enumerable string properties of an object (ignoring properties keyed by symbols), including inherited enumerable properties.

for…of vs for…in

When loop over an Array, unlike for...of, for...in uses property enumeration instead of the array’s iterator. In sparse arrays, for...of will visit the empty slots, but for...in will not.

while

The while statement creates a loop that executes a specified statement as long as the test condition evaluates to true. The condition is evaluated before executing the statement.

let n = 0;

while (n < 3) {
  n++;
}

loop over an object

The prefered way is using Object.entries() or Object.keys() method. It is clean.

const object1 = {
  a: 'somestring',
  b: 42,
};
for (const [key, value] of Object.entries(object1)) {
  console.log(`${key}: ${value}`);
}
// Expected output:
// "a: somestring"
// "b: 42"

Alternative way: You can still use for...in. But it iterates through properties in the prototype chain. This means that we need to check if the property belongs to the object using hasOwnProperty.

Loop Over Set

You can iterate over the elements of a Set using various methods, such as the forEach() method, the for...of loop, or by converting the Set to an array and using array iteration methods.

let mySet = new Set([1, 2, 3, 4, 5]);

mySet.forEach(function(value) {
  console.log(value);
});

Using for...of loop, (but old browser may not support):

let mySet = new Set([1, 2, 3, 4, 5]);

for (let value of mySet) {
  console.log(value);
}

Reference