Rename new .js files to .mjs

src/govuk/i18n.js → src/govuk/i18n.mjs

@@ -1,4 +1,4 @@
-import './vendor/polyfills/Array/prototype/indexOf'
+import './vendor/polyfills/Array/prototype/indexOf.mjs'
 
 /**
  * i18n support initialisation function

src/govuk/vendor/polyfills/Array/prototype/indexOf.mjs

@@ -0,0 +1,27 @@
+(function (undefined) {
+  var detect = (
+    'indexOf' in Array.prototype
+  )
+
+  if (detect) return
+
+  // Polyfill adapted from https://cdn.polyfill.io/v2/polyfill.js?features=Array.prototype.indexOf&flags=always
+  Array.prototype.indexOf = function (searchElement, fromIndex) {
+    fromIndex = Number(fromIndex) || 0
+
+    if (this === undefined || this === null) {
+      throw new TypeError(this + ' is not an object')
+    }
+
+    var array = this instanceof String ? this.split('') : this
+    var arrayLength = Math.max(Math.min(array.length, 9007199254740991), 0) || 0
+    var loopStartIndex = (fromIndex < 0 ? Math.max(arrayLength + fromIndex, 0) : fromIndex) - 1
+
+    for (var i = loopStartIndex; ++i < arrayLength;) {
+      if (i in array && array[i] === searchElement) {
+        return i
+      }
+    }
+    return -1
+  }
+}).call(typeof window === 'object' && window || typeof self === 'object' && self || typeof global === 'object' && global || {})