Can you explain the functionality of this particular line of code in JavaScript?

As I continue to practice my coding skills, despite still being relatively new, I often come across this type of code in loops when searching for solutions to practice problems. I am intrigued by what exactly this particular line of code is accomplishing.

counter[string[i]] = (counter[string[i]] || 0) + 1; 

Furthermore, here is the full code snippet that is utilized to determine the most frequently occurring character within a given string.

var string  = "355385",
    counter = {};

for (var i = 0, len = string.length; i < len; i += 1) {
    counter[string[i]] = (counter[string[i]] || 0) + 1;
}

var biggest = -1, number;
for (var key in counter) {
    if (counter[key] > biggest) {
        biggest = counter[key];
        number = key;
    }
}

console.log(number);

Answer №1

This explanation can be simplified as follows:

If the value of counter[string[i]] is falsy (undefined, 0, empty string, null, etc.), it will default to 0 when adding 1. Otherwise, it will use the existing value to add 1, making this addition the new value for counter[string[i]].

The logic behind this operation utilizes the logical OR operator ||.

For more information on JavaScript variable assignment using the OR operator, check out this source.

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