fix(core): fix type Number in slideToLoop (#5732)

src/core/slide/slideToLoop.js

@@ -4,6 +4,31 @@ export default function slideToLoop(
   runCallbacks = true,
   internal,
 ) {
+  if (typeof index === 'string') {
+    /**
+     * The `index` argument converted from `string` to `number`.
+     * @type {number}
+     */
+    const indexAsNumber = parseInt(index, 10);
+
+    /**
+     * Determines whether the `index` argument is a valid `number`
+     * after being converted from the `string` type.
+     * @type {boolean}
+     */
+    const isValidNumber = isFinite(indexAsNumber);
+
+    if (!isValidNumber) {
+      throw new Error(
+        `The passed-in 'index' (string) couldn't be converted to 'number'. [${index}] given.`,
+      );
+    }
+
+    // Knowing that the converted `index` is a valid number,
+    // we can update the original argument's value.
+    index = indexAsNumber;
+  }
+
   const swiper = this;
   let newIndex = index;
   if (swiper.params.loop) {