JavaScript Statements

✒ Reference: Loops and iteration from the Mozilla JavaScript Guide.

labeled statement

• Provides a statement with an identifier; can be used to identify a loop, then break or continue statements

label :
	statement

• Example of breaking to a label ```javascript let x = 0; let z = 0;

labelCancelLoops: while (true) { console.log(‘Outer loops: ‘ + x); x += 1; z = 1; while (true) { console.log(‘Inner loops: ‘ + z); z += 1; if (z === 10 && x === 10) { break labelCancelLoops; } else if (z === 10) { break; } } }

- Example of continuing to a label

```javascript
let i = 0;
let j = 10;
checkiandj:
  while (i < 4) {
    console.log(i);
    i += 1;
    checkj:
      while (j > 4) {
        console.log(j);
        j -= 1;
        if ((j % 2) === 0) {
          continue checkj;
        }
        console.log(j + ' is odd.');
      }
      console.log('i = ' + i);
      console.log('j = ' + j);
  }

for...of vs for...in

• for...of statement creates a loop Iterating over iterable objects (including Array, Map, Set, arguments object and so on), invoking a custom iteration hook with statements to be executed for the value of each distinct property.
• for...in statement iterates a specified variable over all the enumerable properties of an object.
• Difference between for...of and for...in loop:
  • for...in: Loops through property names of an object. (Returns index when looping through an array; not useful)
  • for...of: Loops through items in an iterable collection (i.e. array)

const arr = [3, 5, 7];
arr.foo = 'hello';

for (let i in arr) {
   console.log(i); // logs "0", "1", "2", "foo"
}

for (let i of arr) {
   console.log(i); // logs 3, 5, 7
}