Efficient mapping of multiple inputs to a single output

Question

Background: I'm thinking of writing a polyfill for KeyboardEvent.key and KeyboardEvent.code.

My proposal is to convert each combination of keyCode, charCode, shiftKey, etc. in the old standard to a key or code in the new standard.

It might look something like this:

function convertToNewKey(event) {
    var key;

    if (event.keyCode === 81 && event.charCode === 0 && shiftKey === false) {
        key = 'q'
    };    
    if (event.keyCode === 81 && event.charCode === 81 && shiftKey === true) {
        key = 'Q'
    };
    if (event.keyCode === 113 && event.charCode === 113) {
        key = 'q'
    };
    if (event.keyCode === 113 && event.charCode === 0) {
        key = 'F2'
    };
    // etc.

    return key;
}

This would require thousands of 'if' statements, and I'm not sure how fast it would run. Key events should be quick to respond to user input.

Is there another way -- such as nested hash maps or dictionaries -- that's easier to write, faster to execute, or both?

Edit: Seems hash maps are faster than 'if', although switch statements are faster than both, at least in some implementations. (Source: jsPerf) I may need to do some of my own speed-testing.

And one more thing: Tip of the hat to Jan Wolter for his research into keyboard events and his script that auto-prints their results.