Setting range in characters, traversing nodes

setRangeOffset.ts

// Filtering SVGElements for TreeWalker
// Filter must be a function in IE, other modern browsers are compliant to this format
export const svgNodeFilter: NodeFilter = ((node: Node) =>
    'ownerSVGElement' in node
        ? NodeFilter.FILTER_REJECT
        : NodeFilter.FILTER_ACCEPT) as any;

/**
 * Range.setStart/setEnd, except it uses offset in characters only
 */
export function setRangeOffset(
    range: Range,
    node: HTMLElement,
    offset: number,
    method: 'setStart' | 'setEnd',
) {
    const {ownerDocument} = node;

    if (!ownerDocument) {
        return;
    }

    const treeWalker = ownerDocument.createTreeWalker(
        node,
        NodeFilter.SHOW_TEXT,
        svgNodeFilter,
        false,
    );

    treeWalker.currentNode = node;

    while (treeWalker.nextNode()) {
        if (treeWalker.currentNode.nodeType === Node.TEXT_NODE) {
            const length = treeWalker.currentNode.nodeValue
                ? treeWalker.currentNode.nodeValue.length
                : 0;

            if (offset > length) {
                offset -= length;
            } else {
                range[method](treeWalker.currentNode, offset);
            }
        }
    }
}