Example 1

In order to square every digit of a number in JavaScript, we can use the following function:

function givenNum(num){
    return Number(('' + num).split('').map(function (val) { return val * val;}).join(''));
}

givenNum(5667);

// outputs 25363649

Explanation and break-down

In order to know what is happening within this function we have to break it down. So, in the first step we split the digits of the number to a string of individual numbers:

function givenNum(num) {
    return ('' + num).split('');
}
givenNum(5667);

// outputs ['5','6','6','7']

Now look at the next step carefully and try to understand. We’ve used the .map() method wherein we’ve used a function as an argument which squares each digit in the number:

function givenNum(num) {
    return ('' + num).split('').map(function (val) { return val * val;});
}
givenNum(5667);

// outputs [25, 36, 36, 49]

In the last step we used join() and encapsulated the whole code with a Number() function so that the final output shows up as a number(25363649) and not as a string(‘25363649’).

Example 2

Now, let’s do the same task thing using a slightly different code:

function squareDigitsOfNum(num){
  return +String(num).split('').map((i) => i*i).join('');  
}

squareDigitsOfNum(776);


// outputs 494936

Example 3

Another way to square the digits of a number is this:

function squareTheDigits(num){
    var string = num.toString();
    var results = [];
    for (var i = 0; i < string.length; i++){
        results[i] = string[i] * string[i];
    }
    return Number(results.join(''));
};

console.log(squareTheDigits(2234));

// outputs 44916