a1111-sd-webui-tagcomplete/javascript/_caretPosition.js

// From https://github.com/component/textarea-caret-position

TAC.getCaretCoordinates = class CaretUtils {
    // We'll copy the properties below into the mirror div.
    // Note that some browsers, such as Firefox, do not concatenate properties
    // into their shorthand (e.g. padding-top, padding-bottom etc. -> padding),
    // so we have to list every single property explicitly.
    static #properties = [
        "direction", // RTL support
        "boxSizing",
        "width", // on Chrome and IE, exclude the scrollbar, so the mirror div wraps exactly as the textarea does
        "height",
        "overflowX",
        "overflowY", // copy the scrollbar for IE

        "borderTopWidth",
        "borderRightWidth",
        "borderBottomWidth",
        "borderLeftWidth",
        "borderStyle",

        "paddingTop",
        "paddingRight",
        "paddingBottom",
        "paddingLeft",

        // https://developer.mozilla.org/en-US/docs/Web/CSS/font
        "fontStyle",
        "fontVariant",
        "fontWeight",
        "fontStretch",
        "fontSize",
        "fontSizeAdjust",
        "lineHeight",
        "fontFamily",

        "textAlign",
        "textTransform",
        "textIndent",
        "textDecoration", // might not make a difference, but better be safe

        "letterSpacing",
        "wordSpacing",

        "tabSize",
        "MozTabSize",
    ];

    static #isBrowser = typeof window !== "undefined";
    static #isFirefox = this.#isBrowser && window.mozInnerScreenX != null;

    static getCaretCoordinates(element, position, options) {
        if (!CaretUtils.#isBrowser) {
            throw new Error(
                "textarea-caret-position#getCaretCoordinates should only be called in a browser"
            );
        }

        var debug = (options && options.debug) || false;
        if (debug) {
            var el = document.querySelector("#input-textarea-caret-position-mirror-div");
            if (el) el.parentNode.removeChild(el);
        }

        // The mirror div will replicate the textarea's style
        var div = document.createElement("div");
        div.id = "input-textarea-caret-position-mirror-div";
        document.body.appendChild(div);

        var style = div.style;
        var computed = window.getComputedStyle
            ? window.getComputedStyle(element)
            : element.currentStyle; // currentStyle for IE < 9
        var isInput = element.nodeName === "INPUT";

        // Default textarea styles
        style.whiteSpace = "pre-wrap";
        if (!isInput) style.wordWrap = "break-word"; // only for textarea-s

        // Position off-screen
        style.position = "absolute"; // required to return coordinates properly
        if (!debug) style.visibility = "hidden"; // not 'display: none' because we want rendering

        // Transfer the element's properties to the div
        CaretUtils.#properties.forEach(function (prop) {
            if (isInput && prop === "lineHeight") {
                // Special case for <input>s because text is rendered centered and line height may be != height
                if (computed.boxSizing === "border-box") {
                    var height = parseInt(computed.height);
                    var outerHeight =
                        parseInt(computed.paddingTop) +
                        parseInt(computed.paddingBottom) +
                        parseInt(computed.borderTopWidth) +
                        parseInt(computed.borderBottomWidth);
                    var targetHeight = outerHeight + parseInt(computed.lineHeight);
                    if (height > targetHeight) {
                        style.lineHeight = height - outerHeight + "px";
                    } else if (height === targetHeight) {
                        style.lineHeight = computed.lineHeight;
                    } else {
                        style.lineHeight = 0;
                    }
                } else {
                    style.lineHeight = computed.height;
                }
            } else {
                style[prop] = computed[prop];
            }
        });

        if (CaretUtils.#isFirefox) {
            // Firefox lies about the overflow property for textareas: https://bugzilla.mozilla.org/show_bug.cgi?id=984275
            if (element.scrollHeight > parseInt(computed.height)) style.overflowY = "scroll";
        } else {
            style.overflow = "hidden"; // for Chrome to not render a scrollbar; IE keeps overflowY = 'scroll'
        }

        div.textContent = element.value.substring(0, position);
        // The second special handling for input type="text" vs textarea:
        // spaces need to be replaced with non-breaking spaces - http://stackoverflow.com/a/13402035/1269037
        if (isInput) div.textContent = div.textContent.replace(/\s/g, "\u00a0");

        var span = document.createElement("span");
        // Wrapping must be replicated *exactly*, including when a long word gets
        // onto the next line, with whitespace at the end of the line before (#7).
        // The  *only* reliable way to do that is to copy the *entire* rest of the
        // textarea's content into the <span> created at the caret position.
        // For inputs, just '.' would be enough, but no need to bother.
        span.textContent = element.value.substring(position) || "."; // || because a completely empty faux span doesn't render at all
        div.appendChild(span);

        var coordinates = {
            top: span.offsetTop + parseInt(computed["borderTopWidth"]),
            left: span.offsetLeft + parseInt(computed["borderLeftWidth"]),
            height: parseInt(computed["lineHeight"]),
        };

        if (debug) {
            span.style.backgroundColor = "#aaa";
        } else {
            document.body.removeChild(div);
        }

        return coordinates;
    }
}.getCaretCoordinates;