Day 24: The for .. of loop

Welcome back to the 24th day of DailyJS. Today’s topic is the for of loop.

You might have seen an exact same thing in some other languages as well. As the name (loop) suggests, it is used to iterate over the iterable objects

• String
• Array
• TypedArray
• Map
• Set
• User-defined iterables

Let’s have a look at the syntax

Syntax

Syntax of the for..of loop is probably one of the easiest things to understand, basically you can iterate over each element of the iterable like this -

const myArr = ['A', 'B', 'C'];

for (const element of myArr) {
    // Do something with the "element"
    ...
    ...
}

Example 1 - Iterating over an Array

Find the sum of all elements in an array using for..of loop

// Iterating over an array

const sumAll = (numbers) => {
    let sum = 0;
    for (const number of numbers) {
        sum += number;
    }
    return sum;
}

const myArr = [1, 2, 3, 4, 5];
console.log ('Sum of', myArr, ' = ', sumAll (myArr));

Example 2 - Iterating over a String

Write a function to reverse a string using for..of loop

const reverseStr = (sentence) => {
    let reversed = '';
    for (const letter of sentence) {
        reversed = letter + reversed;
    }
    return reversed;
}

const myStr = 'Hello World!';
console.log (`Reverse of "${myStr}" = ${reverseStr(myStr)}`);

Example 3 - Iterating over a Map

const myMap = new Map ([['a', 1], ['b', 2]]);

for (const [key, val] of myMap) {
    console.log ('Key: ', key);
    console.log ('Val: ', val);
}

That’s it for today, see you tomorrow :)