KaTeX/contrib/auto-render/splitAtDelimiters.js

var findEndOfMath = function(delimiter, text, startIndex) {
    // Adapted from
    // https://github.com/Khan/perseus/blob/master/src/perseus-markdown.jsx
    var index = startIndex;
    var braceLevel = 0;

    var delimLength = delimiter.length;

    while (index < text.length) {
        var character = text[index];

        if (braceLevel <= 0 &&
            text.slice(index, index + delimLength) === delimiter) {
            return index;
        } else if (character === "\\") {
            index++;
        } else if (character === "{") {
            braceLevel++;
        } else if (character === "}") {
            braceLevel--;
        }

        index++;
    }

    return -1;
};

var splitAtDelimiters = function(startData, leftDelim, rightDelim, display) {
    var finalData = [];

    for (var i = 0; i < startData.length; i++) {
        if (startData[i].type === "text") {
            var text = startData[i].data;

            var lookingForLeft = true;
            var currIndex = 0;
            var nextIndex;

            nextIndex = text.indexOf(leftDelim);
            if (nextIndex !== -1) {
                currIndex = nextIndex;
                finalData.push({
                    type: "text",
                    data: text.slice(0, currIndex)
                });
                lookingForLeft = false;
            }

            while (true) {
                if (lookingForLeft) {
                    nextIndex = text.indexOf(leftDelim, currIndex);
                    if (nextIndex === -1) {
                        break;
                    }

                    finalData.push({
                        type: "text",
                        data: text.slice(currIndex, nextIndex)
                    });

                    currIndex = nextIndex;
                } else {
                    nextIndex = findEndOfMath(
                        rightDelim,
                        text,
                        currIndex + leftDelim.length);
                    if (nextIndex === -1) {
                        break;
                    }

                    finalData.push({
                        type: "math",
                        data: text.slice(
                            currIndex + leftDelim.length,
                            nextIndex),
                        rawData: text.slice(
                            currIndex,
                            nextIndex + rightDelim.length),
                        display: display
                    });

                    currIndex = nextIndex + rightDelim.length;
                }

                lookingForLeft = !lookingForLeft;
            }

            finalData.push({
                type: "text",
                data: text.slice(currIndex)
            });
        } else {
            finalData.push(startData[i]);
        }
    }

    return finalData;
};

module.exports = splitAtDelimiters;