Java vs JavaScript: enhanced for loop and forEach() explained

Java for-each / enhanced for loop

syntax

for(dataType variable : collection){

}

• Used to iterate over arrays and collections.
• Simple and more readable than traditional loop.
• No need to use index of elements.
• Provide only values not indexes
• Always iterating over all elements from first to last.
• Can use break or continue

Limitations

• Cannot iterate in reverse order
• Cannot directly access the index of element
• Cannot modify elements directly

example with array

int numbers[] = {1,2,3,4};

for(int num: numbers){
  System.out.println(num);
}

example with collection

List<String> names = Arrays.asList("Dog", "Cat","Elephant");

for(String name: names){
  System.out.println(name);
}

Java forEach() method

• Not a loop; Method provided by Iterable interface
• Cannot use break or continue
• Can modify elements

List<String> names = Arrays.asList("Dog", "Cat","Elephant");
names.forEach(System.out::println); // used method reference

List<String> names = Arrays.asList("Dog", "Cat","Elephant");
names.forEach(name -> System.out.println(name)); // used lambda function

JavaScript for-each / for ….of / enhanced for loop

syntax

for( const variable of array){

}

• Used to iterate over arrays, strings, maps, sets
• Simple and more readable than traditional loop.
• Provide only values not indexes
• Can use break or continue

Limitations

• Cannot iterate in reverse order
• Cannot directly access the index of element

example with array

const numbers = [1,2,3,4];

for(const num of numbers){
  console.log(num);
}

const names = ["Dog", "Cat", "Elephant"];

for(const name of names){
  console.log(name);
}

JavaScript forEach() method

• Cannot use break or continue or return
• Can access index
• Can modify elements

const names = ["Dog", "Cat", "Elephant"];
names.forEach(name => console.log(name));

JavaScript for ….in loop

syntax

for(const key in object){

}

• Used to iterate over enumerable keys
• Provide only keys not values
• Best for objects, not recommended for arrays
• Can use break or continue

const person = {
    name: "Harry",
    age: 59
};

for (const key in person) {
    console.log(key + " > " + person[key]);
}