What does this specific line of code mean/do in Javascript

Question

I'm practicing my coding and I'm still kind of new. While looking for solutions to practice problems I see this kind of code used in loops and I'm curious what this line of code does.

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

here it is in the full code that is used to count most occured character in a string if this helps

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);

Potentially a duplicate of [What does the construct x = x || y mean?](http://stackoverflow.com/q/2802055/218196) — Felix Kling, Dec 17 '16 at 23:15

score 0 · Accepted Answer · edited May 23 '17 at 12:08

0

It is basically saying

If counter[string[i]] is falsy (undefined, 0, empty string, null etc) use 0 to add to 1 otherwise use its existing value to add to 1 and make this addition the new value for counter[string[i]]

It is using the logical OR operator ||

See JavaScript OR (||) variable assignment explanation

edited May 23 '17 at 12:08

Community

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answered Dec 17 '16 at 23:11

charlietfl

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What does this specific line of code mean/do in Javascript

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