Function addKeyframeToScript

packages/parsers/src/gsapParser.ts:2138–2254

(
  script: string,
  animationId: string,
  percentage: number,
  properties: Record<string, number | string>,
  ease?: string,
  backfillDefaults?: Record<string, number | string>,
)

 * object. If the percentage already exists, its value is replaced.
 */
export function addKeyframeToScript(
  script: string,
  animationId: string,
  percentage: number,
  properties: Record<string, number | string>,
  ease?: string,
  backfillDefaults?: Record<string, number | string>,
): string {
  let loc = locateAnimationWithFallback(script, animationId);
  if (!loc) return script;
  let kfNode = findKeyframesObjectNode(loc.target.call.varsArg);

  // Array-form keyframes can't host an arbitrary new percentage — normalize to
  // object form in place first. (convertToKeyframesInScript below only converts
  // FLAT tweens; it early-returns when keyframes already exist.)
  if (!kfNode) kfNode = convertArrayKeyframesToObjectNode(loc.target.call.varsArg);

  if (!kfNode) {
    script = convertToKeyframesInScript(script, animationId);
    loc = locateAnimationWithFallback(script, animationId);
    if (!loc) return script;
    kfNode = findKeyframesObjectNode(loc.target.call.varsArg);
    if (!kfNode) return script;
  }
  const pctKey = `${percentage}%`;

  const newValueNode = buildKeyframeValueNode(properties, ease);

  // Merge into existing keyframe at this percentage, or insert new
  const existing = findKeyframePropByPct(kfNode, percentage);
  if (existing) {
    if (existing.prop.value?.type === "ObjectExpression") {
      const existingRecord = objectExpressionToRecord(existing.prop.value, loc.parsed.scope);
      const merged = { ...existingRecord };
      for (const [k, v] of Object.entries(properties)) merged[k] = v;
      existing.prop.value = buildKeyframeValueNode(
        merged as Record<string, number | string>,
        ease ?? (typeof existingRecord.ease === "string" ? existingRecord.ease : undefined),
      );
    } else {
      existing.prop.value = newValueNode;
    }
  } else {
    // Build the new property node with a quoted percentage key
    const newProp = parseExpr(`{ ${JSON.stringify(pctKey)}: {} }`).properties[0];
    newProp.value = newValueNode;

    // Insert in sorted order by percentage
    let insertIdx = kfNode.properties.length;
    for (let i = 0; i < kfNode.properties.length; i++) {
      const key = isObjectProperty(kfNode.properties[i])
        ? propKeyName(kfNode.properties[i])
        : undefined;
      if (typeof key === "string" && percentageFromKey(key) > percentage) {
        insertIdx = i;
        break;
      }
    }