Javascript: meaning of || operator while initializing var

Question

to get information about what key was pressed, I now use following code:

function AddEventListeners() {
    document.getElementById('txtHangman').addEventListener('keypress', TextHangman.bind(this), false);
}

And then the eventhandler function:

function TextHangman(_key) {
    var _keypressed = _key.which || _key.key;
}

The code works and gives me the information I want but I don't understand what the || operator does when initiliazing the var _keypressed. Some explanation would be great.

Thanks!

G

Answer 1

It means the same as it does everywhere else. It does nothing special when used near a var statement.

If the left hand side evaluates as true (i.e. not 0, undefined, etc), it evaluates as the left hand side.

Otherwise, it evaluates as the right hand side.

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Precedence rules means it gets resolved before the assignment.

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Essentially the code is the same as:

if (_key.which) {
    var _keypressed = _key.which;
} else {
    var _keypressed = _key.key;
}