primrose/src/reverse.js

Syntax-highlighting text editor that renders to an HTML5 Canvas element

const combiningMarks =
    /(<%= allExceptCombiningMarks %>)(<%= combiningMarks %>+)/g,
    surrogatePair = /(<%= highSurrogates %>)(<%= lowSurrogates %>)/g;

// unicode-aware string reverse
export function reverse(str) {
    str = str.replace(combiningMarks, function (match, capture1,
        capture2) {
        return reverse(capture2) + capture1;
    })
        .replace(surrogatePair, "$2$1");
    let res = "";
    for (let i = str.length - 1; i >= 0; --i) {
        res += str[i];
    }
    return res;
}